AR15 Primer – A Beginner’s Guide to “America’s Rifle”


The modern consumer AR15 is an amazingly diverse system. Besides its storied history, one of its main attractions is its modular design. Almost every part of this weapons system is easily replaceable. No other platform has as much aftermarket support in the market today. It can be configured as a long range precision instrument, or a close quarters combat (CQB) pistol or short barrel rifle (SBR). It can be chambered for a wide range of calibers from the venerable .22lr to a .50 Beowulf. Early AR15s and their M16 counterparts are 20” rifles. The majority of AR15s in the commercial market today are 16” or shorter “carbines”. Extremely strong aftermarket support, and standardized parts interchangeability make this platform extremely popular with many consumers.

However, since there are so many configurations and  so many different looks, many new consumers are overwhelmed with the choices that they face. To address this, I’ve written this document to help the first time consumer become an informed consumer. A little knowledge goes a long way to help you spend your hard-earned money. My sole wish is to provide you with enough background and general information to make a smart buy, and I will try to remain as objective as possible. I would also like to say that this is a general overview and I will not go in depth with every explanation. I do hope that after reading this, you come away with a good understanding and appreciation of the AR15.

I would also like to give thanks to my friends Dieselpower from, and Quentin from for their help and suggestions. Special thanks to my good friend and cousin Connie for her time and effort in  of my incoherent ramblings.


AR15 PrimerThe AR15 was developed in the 1950s by Eugene Stoner as a lightweight 5.56x45mm version of the AR10 7.62 NATO. The first AR15 was made in 1959. It was intended to be a lightweight rifle that shot a lightweight round, so that infantrymen could carry more rounds per loadout when going into battle or patrol. More historical information can be found here:


The modern day civilian market AR15 is a semi automatic firearm. The original AR15 was a select fire (automatic) weapon that was intended for military use only. Please be aware that AR15s marketed as an M4 are not truly M4s unless they have select/automatic lower receivers with automatic fire control groups, and 14.5” barrels with carbine gas systems. M16s are also select fire/automatics with 18” or longer barrels with rifle gas systems and usually a carry handle on the upper receiver. Unless you are in a state that allows NFA gun ownership, and you are willing to wade through and then wait for all the paperwork to process, you will not be able to get an authentic automatic M4 or M16. Everything else is an AR15, no matter what’s stamped on the receiver.


First question you should ask yourself is: “How am I going to be using this rifle.” Your “intended use” will govern what style and what options would be more important to your choice. It should include what kind of shooting you intend to do, and at what distances. If you live in the city and can only shoot at a rifle range, you will be limited to the distances available at your range. If you want to use this gun to shoot prairie dogs at 500 yards, then your choices may be vastly different compared to the intended use for home defense. Put simply, if you want to target shoot at 1000 yards you can do it, but its not going to be the same AR as a home defense rifle.

Second question you should to ask yourself is: “Do I buy a complete AR or make one?” This is a purely subjective question. I feel that if you are comfortable fixing a bicycle or assembling Ikea furniture, you can build at least the lower receiver by yourself. It’s really not that difficult. You will get the added benefit of learning the inner workings on how your AR works. It is just a simple machine. There is nothing mysterious about it. Installing a barrel on the upper receiver is a bit different as it requires more specialized tools, but if you opt to build your own lower receiver and purchase a complete upper receiver you may be able save yourself some money. You will learn a lot about how your gun functions, and you will be able to choose every single component in your rifle.

Purchasing a complete rifle is a valid choice, and many people do choose to go this route. The main benefit is that you don’t have to spend any time putting it together and it comes with a manufacturer’s warranty. (Keep in mind though, if you want warranty work done on it, you most likely will have to ship your rifle in and will be without a firearm.) Competition is pretty fierce nowadays, so if you shop around you can find an AR15 complete for pretty much the same price if not cheaper than what you can build it for.

My personal recommendation is to purchase a stripped lower from a local guns store (LGS) and then purchase parts online and looking for the best deals based on exactly what you want. I also personally try and purchase locally as much as possible. If the price difference is under 10% I will generally purchase locally. You may or may not decide to do the same but it’s nice to have a gun shop close by. Again this is my personal preference; please don’t take this as something you must do.


The main factors that you should consider in your decisions are: need, weight and cost. To increase your happy quotient, make choices to maximize meeting your needs, while minimizing cost and weight. Remember, every choice you make, entails tradeoffs: Cost, precision, weight, reliability, utility. Keep this in mind when you making your decisions!


Weight is the enemy! You can hang every possible gizmo and gadget on your AR and have one blinged out, super sexy, radical tactical, ultra mall ninja 15 pound beast! Or you can have an AR that weighs just 7 pounds and does everything you need it do.


The most common AR15 would be the M4 type 16” barreled carbine, affectionately known by many as the M4gery. It is modeled after a standard issue military m4 carbine with the exception of a mandated 16” minimum overall length barrel and semi automatic fire controls. It can come with carry handle type upper receiver or a flat-top upper with a 1913 rail. It features a collapsible stock and a non-free floated seat of carbine length hand guards. This style is very popular, and is good for most types of shooters. Range shooting, plinking, varmint hunting, competition, home defense, and service (law enforcement/military) types all use this style. It features a carbine length gas system (7” gas tube). This is the type you most commonly see in t.v. or movies. It is what most people think of when you say M16 or M4. If you are interested in just general use/plinking under 300 yards, this is the type that is the cheapest and most readily available. With a decent barrel and decent ammunition, a good AR will give you to 2-3 MOA (2-3” inch groups @ 100 yards). With a great barrel, match grade ammunition, and a good shooter, you can expect 100 yard groups easily be 1 MOA and under (one inch groups @100 yards). I would generally recommend this type of AR15 for most shooters, with an exception of the gas system. I personally prefer mid-length gas systems; I will expand on this later.

Long Range Precision / Varmint types:
If you are opting for a more specialized use that requires more precision than your average AR, this is the type of AR you should be looking at. These ARs are precision-oriented and make tradeoffs on cost and weight to achieve greater accuracy and precision. Usually the first thing that separates them from M4gerys is the barrel. In this instance, a longer barrel is chosen with different twist rates and made from different materials. Varmint types might even have slower twist rates which are optimal for shorter/lighter projectiles used for varmint hunting. The second thing that sets them apart is choice of hand guards. Precision-oriented builds will all invariably have free floated hand guards. This means the hand guards (whether tube type or railed type) do not touch the barrel throughout the entire length of the barrel. It floats around the barrel and is only attached to upper receiver or sometimes the barrel nut. Having the hand guards free floated allows your rifle to be more consistent as it protects the barrel from any pressure and movement that may change your point of impact. Beside any aesthetic preferences, hand guards can add a little weight and are usually more expensive than your average plastic hand guards. Stocks for these builds are usually bigger and adjustable to provide better check weld, stability and balance for these heavier styles.

SBR/Pistol builds:
For the sake of brevity, I’m only going to touch upon these types of AR15. Please check your local laws as to the legality of ownership of these specific models. These types are generally suited for close quarters use (less than 100 yards). I personally love these types of ARs but there are tradeoffs you must consider when purchasing them. First off is cost of ownership. SBRs (short barreled rifles) are any rifle with a overall barrel length shorter than 16 inches or has an overall length of 26 inches with the stock fully collapsed or folded. You must file paperwork and wait upwards of 2-4 months, and then purchase a tax stamp in order to legally own an SBR. Pistols don’t require this paperwork but may have additional restrictions that you must research in your state. This may seem a lot of hoops to jump through, but when you are done you will have a shorter lighter weapon that handles much better, and lets you track and transition much faster. There are drawbacks however. The main disadvantages are decreased muzzle velocity and increased muzzle blast (noise and flash).

Competition builds:
Since this guide is for a beginner, I will only briefly explain this type of AR. A competition model is a highly specialized AR that is designed to give any the user any advantage of speed and accuracy. They vary in length and twist to compliment what the user needs. They are usually made with a specialized trigger (light and short) and specialized optics. I usually don’t recommend this type to any first time AR owner as they are usually very expensive and very specialized.

At this point, you should have a general idea on how you plan on using your AR. I recommend that you first figure out your intended use, then start looking for a barrel that will suit your needs.


Disclaimer: Again for the sake of simplicity and brevity, I will only be referring to the most common 5.56×45 NATO chamberings. Many other calibers are available for the AR but I will not get into them. I will also not get into short barreled rifles or suppressors as usually it is not a choice that most first time buyers make. Both these thing will require you checking if they are legal to own in your locale and require copious federal paperwork that will require are few months wait. I will say that SBRs and supressors are great choices, but you need to research elsewhere and decide for yourself if they are the right choice for you.

5.56 x 45 NATO vs .223 REMINGTON:

With a 5.56 chambered barrel, you can use both .223 Remington and 5.56 nato.
With a .223 chambered barrel, you can ONLY use .223 Remington safely.
There are other hybrid chamberings available, such as the Wylde, that are found on precision type barrels that will also work with both types of ammunition. Find out what the AR you are about to purchase is chambered in first before buying it!


The 5.56 x 45mm NATO chambering is a good choice for HD/SD and general purpose type shooting. It features “looser” tolerances that give improved reliability and is made to withstand higher pressures associated with the 5.56 NATO round. It is not a match grade chambering as is not a good choice for precision shooting. It is also the most common AR chambering available. It is the most common choice for military, law enforcement and duty type configurations.  For more information please refer to

A .223 Remington chambered AR is not as common as the 5.56 NATO. It features a tighter chamber better suited for precision shooting. Please only use .223 ammunition with this chambering. Using a higher pressure 5.56 round may cause injury to both yourself and your rifle.

The Wylde chamber is probably the most common of the hybrid chamberings. It was originally designed as a match grade chambering that would allow the use of long 80 grain bullets. It was later found to be compatible with both .223 and 5.56 commercial ammo and found to be more accurate than a standard 5.56 chamber. It is a very good choice for a precision-oriented build or long distance shooting. There are many other hybrid chamberings all with their own unique advantages and disadvantages.


This means, the most important parts of your AR is NOT the 64x scope, or the 18″ free floating rail, or the super sniper 10 position pneumatic stock.  The most important parts of your AR is the barrel and the bolt.  So let’s start off by first choosing the right barrel for you. The barrel is probably the most important and most overlooked component in your AR. Most people don’t even look at the barrel; they are busy looking at the acres of rail space on the hand guards or the collapsible stock, or all the lights and lasers and optics hanging off the rails. Stop what you are doing.  Look at the barrel first, and pick the best barrel for your intended use.  Everything else is just icing on the cake.

Your average AR15, with a 14.5 to 16” barrel will quite easily go out to 400 yards.  A decent AR with a great barrel should be able to shoot 1 MOA or less in the ideal conditions (bench rested, capable shooter, adequate optics and optimal ammunition). Most recreational shooters can expect to be happy with 2-3 MOA (2-3 inch groups at 100 yards) with plinking ammo with the same setup.


So as an average consumer you must keep in mind that your total barrel length must be at least 16” inches long. The total length of your barrel and muzzle device (flash hider (FH), muzzle brake, or compensator) is used. You may purchase a 13.7” barrel and have a very long muzzle device (such as a Noveske KX3) pinned and welded to it to get it to the 16” overall length. Or you may opt for a 14.5” barrel, with a muzzle device, pinned and welded to it, to bring overall length to 16”. Most manufacturers offer 16” barrels, which do not require the muzzle device to be permanently attached (read pinned and welded). Some builders offer shorter barrels with the muzzle device already permanently attached to it.

Please be careful, some states have additional requirements as to what type of muzzle device can be used on your rifle. Please check local and state laws before you purchase. A permanently attached muzzle device may be removed by a competent gunsmith but the muzzle device may be destroyed or damaged in the process. Also there is a chance that the barrel will be damaged in the process.

As a first time buyer, I would recommend that you go with a 16” barrel (over a shorter length). This way if you decide to later on change your muzzle, it will be very easy to do. I personally like compensators, but I would recommend that you start with the basic A2 flash hider (if legal). This is because it is inexpensive and your basic 5.56 and .223 has relatively mild recoil. The 16” barrel is versatile enough to provide short and medium range capabilities. A shorter barrel would only provide a moderate decrease in weight and modestly better handling characteristics while minimally decreasing muzzle velocity.

So now that you know that you need at least a 16” overall length barrel, how long a barrel should you get? Many people assume that the longer the barrel the more accurate it will be. This is not necessarily true. Not to get overly technical, but usually a shorter barrel is more precise due to it being stiffer and less susceptible to barrel whip (with all other factors being equal). The main advantage with going with a longer barrel is muzzle velocity. The longer the barrel, the more time you have to burn all the powder and the more time your bullet gets to accelerate. The faster you get your bullet going, the faster it gets to target giving it less time to be affected by other environment factors (like gravity and wind).

Your average M4 style 16” carbine is good for short and intermediate distances, (0-400 yards). At longer distances 300+ yards and up), the common 55 grain (gr) full metal jacket (FMJ) becomes very susceptible to shifts in point of impact due its light weight. You will notice with the 55 gr pill, pronounced drop and windage especially at mid to long ranges.

For longer distances you want your bullet to be going as fast as possible so you can be as accurate as possible. Also increasing muzzle velocity increases the energy the bullet has to transfer to and incapacitate the target.  Also for long distance shooting you want your bullet to be as heavy as possible with the highest BC (ballistic coefficient) so that it is resistant to changes in trajectory by wind. All things being equal, a heavier bullet loses less energy over a given distance than a comparable lighter weight bullet.   So for longer ranges you should consider a heavier and longer projectile, like a 69 gr, 77gr, 80 gr etc.  For those bullets, a faster twist rate (1×8 1×9) is needed to stabilize the projectile. Long distance shooting is usually not for your average first time buyer. There are a lot of other factors and decisions that must be made for long distance precision builds that are best left for more experienced shooters.

If you opt for a 18” or 20” barrel, you gain muzzle velocity and sight radius while trading off weight and handling. Longer barrels are usually found in mid to heavier profiles, and can significantly add weight to the front end.  Heavier profiles are usually only found on range / benchrest type rifles as their significant weight makes them unweildy.  One benefit of rifle lengths is that the gas system for rifles is noticeably smoother than shorter systems. The powder has time to burn evenly and completely. The gas produced has a lot more room to expand, and by the time it gets to the gas port it can cycle the BCG much more smoothly and evenly (more on this later)


The longer the projectile, the faster the twist is needed in the barrel. I will make a generalization here and refer to bullets by their weights.  For the most part the over length of a bullet corresponds to its weight, but this is not always the case.  If the bullet it made out of a less dense material its over size and length will be longer than advertised by its weight.

Nowadays, the most common rate is 1×9 (one twist per nine inches), which is optimal for stabilizing 55 grain FMJs. 1×9 means one full revolution (twist) every 9 inches. This twist will adequately stabilize and 62-69 grain bullet but may have trouble with the heavier/longer 75 grain and up bullets. I cannot be exact here because every barrel manufacturer is different, and every barrel is different. This is just a general guideline.

The second most common twist is 1×7. Most milspec barrels are 1×7 because they need to stabilize the very long tracer rounds. It will adequately handle a 55 grain projectile. And handle 80 grain bullets and everything in between.  It may have trouble with and is not the best choice  for very short projectiles i.e. 40 and 46 grain projectiles.

The third most common twist is 1×8. This is usually used by precision oriented stainless barrels. The most notable exception is S&W’s MP15, which uses this rate. My personal belief is that this is a great middle of the road rate and should be used more often. It handles the 55 grain projectiles well as well as everything up to 77 grains. You would need to test it out for yourself. It’s optimal at about the 67 grain size.

There are slower twist barrels such as 1×12 twist. These barrels are optimal for smaller projectiles, like 36 and 40 grain bullets. These are usually for varmiters that use specialized bullets for their hunting needs.


  • CMV Chrome Molybdenum Vanadium
  • 4150 type a steel used in making barrels
  • 4140 type a steel has 10% less carbon than 4150
  • CHF Cold Hammer Forged
  • BFH Barrel Forged Hammer (same as CHF)
  • HP / HPT high pressure tested
  • MP magnetic particle tested
  • CL chrome lined
  • SS stainless steel

These are different terms when describing barrel features. Honestly, for your average range gun and plinker, you do not need CL or HP MP barrels. If you only plan to shoot a couple hundred rounds a year, a CMV or 4140 barrel is more than adequate and will probably last you a lifetime.

4150 has 10% more carbon than 4140. Metal with more carbon is usually harder but trades flexibility for that hardness. It is debatable if 4150 is better than 4140. These numbers by themselves are really just stats and are not indicative of the overall quality of the barrel.

If you go through a couple thousand rounds a year, you might want to invest in CL barrels as they will last 3-5x longer. Chrome lining will slightly decrease precision of your barrel, but it is a very small loss. It will also cost a little more, but your barrel and chamber will last a lot longer and be easier to clean.

An alternative to chrome lining is ferritic nitrocarburizing (FNC) aka Tennifer and Melonite. So far I am only aware of manufacturers like S&W and LWRC using this process on AR barrels. This process treats the actual surface of the barrel, unlike chroming. It is a case hardening process that infuses carbon and nitrogen into the metal itself. Many tests have shown that FNC creates a surface that is harder than chrome and resists corrosion better too. FNC has a great track record with pistols as is the case with Glock’s legendary Tennifer finish. It remains to be seen if it can handle the higher velocities and pressures associated with rifle rounds.

Besides cost, chrome’s only downside is that it applies to the surface. Since it is nearly impossible to lay down a completely even layer of chrome, chrome-lined barrels are usually not as precise as they were before chroming. This is not to say that chrome lining a barrel will make it inaccurate. If you take a stellar barrel and chrome it, it will still be a stellar barrel. It will be just a little less precise and a whole lot more durable. Conversely, if you take a crappy barrel and chrome line it, you now have a crappy barrel that will stay with you forever.

There are two main downsides to FNC. First, since it is relatively new, and although it was tried and tested in pistol caliber barrels, it doesn’t have long history or track record with the higher velocities and pressures associated with rifle calibers. Second, FNC is a highly toxic process. This means it is harder to set up and maintain the equipment required for this process. So facilities that offer this service are uncommon.

Many people are saying that FNC is the wave of the future and that FNC will replace chrome in a few years. I believe that it looks very promising, but only time will tell if it will be a viable option.

If you need a service type weapon or just want a dead nuts reliable weapon for SD/HD purposes, you will want to invest in a barrel that is HP AND MP tested. HP and MP testing is added insurance. It will greatly reduce the chance your barrel will be rendered inoperable by voids and inclusions undetectable by the naked eye.

CHF and BFH describe a manufacturing process that produces a great service type barrel. Please note, CHF is not optimal for precision type builds. The CHF process makes a very strong durable barrel perfect for high round count shooting, and duty/HD type roles. I personally think that it is worth the additional cost, but I don’t see it necessary for a plinker or light use weapon.

Stainless Steel (SS) barrels are usually found in precision type barrels. SS trades off wear and corrosion resistance for more precision and accuracy compared to CL and harder steel barrels. They also tend to erode faster and will not last as long as other types of barrels. Most commonly found on varminting, hunting and long range setups, SS is not a good choice for high round count weapons.

Please keep in mind that all barrels wear out due to usage. While a CL barrel might last longer, by 40k rounds, it’s not as precise as it was when it was new. Precision barrels might only last 10k rounds but some shooters might change them out it by 4k rounds because their needs are no longer being met due to wear and erosion. Also overheating your barrel will wear it out faster. If you like to dump magazine after magazine, your barrel will wear out faster than if you slow fired the same number of rounds.

One very important thing to remember about barrels; please don’t think that every CHF barrel or 4150 or SS barrel is the same. Different barrel makers will have different recipes for steel even if they are all considered 4150 or CMV or 4140 etc.  There are different grades and qualities of 4150 CMV and 416 SS.  There are different ways to rifle and chrome barrels. There are different ways to measure headspace and to do quality control inspections. What you are paying for is all the expertise, craftsmanship, and quality control that a particular barrel maker utilizes when making your barrel. Please remember the old adage: You get what you pay for.


The three main types of contours are LW light weight, Med Con medium contour, and Heavy (Bull barrel / Hbar). The stiffer the barrel, the more accurate/precise it tends to be. Heavy contours are best utilized for bench rest shooting or fire suppression roles. They soak up a lot more heat, so you can get more rounds through it before groups start to open up or the barrel overheats. On the downside, they take longer to cool down and they are heavy to carry and hold steady while shooting free hand. Interesting note, heavy contours are cheaper to make than other contours. This is because other contours take more machining time to pare down or shape from the blanks they are made from.

Medium contours like the M4 contour are probably the most widely available. The M4 style has a cutout in its profile that is there to allow you to mount a grenade launcher. Unfortunately, the average consumer is not allowed to have destructive devices, like a grenade launcher, for example. The M4 contour is a little lighter than other medium contour types. There are many other kinds of medium contours and are arguably the most popular, as they provide a good balance between rigidity and weight in relation to either extremes.

LW builds (my personal favorite) make great service type carbines. They are easy to handle, carry and shoot. But they will show their downsides if you are ever in an extended firefight (or just doing multiple mag dumps). Also, they are not the best choice for precision builds due to relative flexibility. If you are building a range/plinker, a LW or medium contour is just right for you.

Special note to all builders, please take note of the diameter of the barrel around the gas port. You will need to match your gas block to this measurement.


The majority of barrels made for AR15s have the extensions already on them. The extension is located on the end opposite of the muzzle that goes into the upper receiver. It is affixed to the receiver with the barrel nut and houses the chamber. High round count barrels will exhibit throat erosion, which can lead to dangerous shooting conditions. When buying a used barrel or upper, it’s always a good idea to use a headspace gauge or have a professional check it out. Go/ no go gauges are relatively cheap and are a good addition to your specialized tools inventory. Also chrome-lined chambers are usually more desirable as they are easier to clean out and more durable than standard parkerized versions.


My personal take on this is that, since M4 feedramps cost the same as non M4 type, why not get them. It is debatable whether or not they will make your AR feed more reliably. As a general rule of thumb, make sure you match your upper receiver type to the ramp type of your barrel extension. So match non M4 to non M4 and M4 feedramps to M4 feedramps. While you can get away with M4 ramps on your barrel extension and non M4 upper, you won’t be able to get away with using M4 feedramp type upper and non m4 feedramps on your extension. This combo M4 feedramped upper with Non M4 ramped extension will give you failure to feed problems.

There is some debate on M4 ramps. One valid argument advocates only using upper receivers without feedramp extensions. This gives the benefit of being able to use regular rifle ramps and m4 ramped barrel extensions. If you plan on changing barrels often, this may be a viable option for you. This is a valid argument especially if you plan on changing barrels. There have been reports of people running into issues with their receiver ramps not lining up with the ramps on the extension of their new barrels.


The bolt is housed within the bolt carrier assembly. These are the parts that cycle back and forth within the upper receiver every time your fire your AR. When you pull the charging handle back, you are essentially pulling the BCG back and out of battery. When you release the charging handle, the BCG springs forward over the magazine well, picks up a new round, and puts the round into the chamber. The bolt holds the round in place ready for you to pull the trigger, which releases the hammer. The hammer strikes the back of the firing pin pushing it through the bolt to strike the primer on the round thereby firing it. The bolt is subjected to the highest amount of stress in your AR.

Get a good bolt. Don’t choose the cheapest option. If your bolt breaks, your gun goes down. Bolts are subjected to the highest amount of stress in your AR. Carpenter 158 steel is mil-spec should be considered minimal for any service level grade AR. Bolts are relatively cheap. It is only $50 for a good one. Please don’t skimp on this part. MP/HP testing should be a requirement for everyone’s build. Chromed or coated bolts and BCGs are nice but not necessarily needed. Coated units definitely make cleaning easier, but won’t necessarily make your bolt any more reliable than it already is. A regular parkerized bolt will do the job just fine. I would also recommend that you get a spare bolt, extractor, extractor spring and firing pin in your bag of tricks.

BCG (bolt carrier group) is the term for the whole assembly which includes the firing pin, bolt, and housing. The carrier usually doesn’t wear out and can be reused. When deciding between a semi auto (SA) and full auto (FA) carrier for semi automatic applications, either one will do the job. FA carriers are made heavier because more mass is needed to slow the cycling rate of full auto applications. Heavier does not necessarily mean better in this instance though. Most FA carriers also have a small shroud that protects the firing pin from hitting the hammer when the BCG cycles back and cocks the hammer. For SA guns, this difference is negligible and in some cases unwanted. There are applications (mostly for competition guns) where some users actually want the fastest cycling possible and opt for light weight BCGs. My personal opinion is that since most factory guns are overgassed, I would prefer a full auto carrier for the added mass and for the shroud protecting the firing pin. Interestingly enough, having a FA carrier doesn’t make your gun automatic nor is it really necessary for all FA guns.

Insist that the gas key bolts of your BCG are properly staked. It’s added insurance to keep your gas key secure, thusly preventing any stoppages. Some manufacturers insist that staking is not needed (i.e. Young’s) but it’s really not too difficult to do yourself if needed.


There are 2 major types of gas systems that the AR runs on. The first being DI (direct impingement) and the second being piston. DI is the original design. Piston is a relatively new development. There have been forays into piston designs in the past, but it’s only been recently that piston driven ARs have been become popular. The best thing I can do you is show you the pros and cons a piston system offers, it’s your personal choice to decide if it fits your needs. Please understand that since there is no set standard for a piston system, every piston system is a proprietary design that will require different and non interchangeable parts.


  • A cleaner running system. (less fouling of the BCG and chamber, more fouling by the gas block or exhaust)
  • Should be more reliable in adverse shooting environments.
  • Should be easier to clean, (provided you don’t need to remove the hand guards)


  • Costs more than a comparable DI setup
  • Weighs more than a comparable DI setup
  • Harsher recoil impulse (I concede that this is subjective and debatable)
  • Inherently less accurate,(minor)
  • Slower follow up shots (minor)
  • Proprietary parts make it harder, costlier, and longer to replace broken parts.

Personally, I would only recommend a piston setup if you where looking for a non precision type carbine and need the extra reliability due to your expected shooting environment.

DI gas systems come in 4 flavors: Rifle, mid-length (middy), carbine, and pistol. The most common types are carbines, with 7” handguards. The next most common types are rifles with 12” of rail. Relatively new developments are midlengths with 9” handguards. Pistols are uncommon and I won’t be going too much into them. Only consider rifle length gas systems for 18+ inch barrels. Both carbine and midlength gas systems can be used for 14” to 16” length barrels. For these lengths, I usually recommend midlengths as their advantages outweigh their disadvantages:

  • Weight: Advantage Carbines. Since the midlength rail/hand guard and gas tube is 2´ longer, it weighs more, not much more, but carbine gassers are clearly lighter.
  • Sight Radius: Advantage Middy. Being able to put the front sight 2” farther from the rear sight is a clear advantage. The longer the better.
  • Longer hand guard rail: Advantage Middy. I admit this is a subjective point, but unless you have freakishly short arms, the carbine length guards are going to be really short for you. Even my 5”1” wife likes the length of the mid length over the carbine.
  • Aesthetics: Advantage Middy. Again purely subjective, and you may disagree with me on this point, but to me a carbine looks unbalanced with the exposed barrel being too long.
  • Costs are about the same for either option. Draw

People point out that since the gas port is so much farther away from the chamber and gas pressure should be lower, middies should be inherently smoother and easier on all the reciprocating parts of your carbine. While I agree with this in theory, I’ve personally found that most middies are overgassed. So this makes the whole “less recoil, smoother impulse” debate a moot point. Most builders overgass systems in order to cycle the cheap under-powered target and plinking ammo. I’ve personally shot a few middies that were over gassed and they recoiled harder than carbines, and vice versa. Gassing is dependant on how the gas port is sized. As a consumer, you really don’t have any control over the gas port sizing of your barrel or have any way to check or measure it, unless you order a custom barrel for your build. Also since it’s better to have a slightly overgassed system (feed all power levels of ammo) as opposed to an undergassed system (only feeds higher powered ammo), I will call it a draw.

So in my humble opinion, for the minor inconvenience of a few extra ounces of weight, you get a lot more in return with midlengths.

Please understand that once a gas port is drilled into the barrel, it is very difficult and expensive to change from a carbine to a middy or vice versa. If you have a carbine gas system, don’t worry too much. If you want a longer rail or hand guard, it is relatively easy to swap out the gas block to a low profile model or modify a front sight base.This allows you to free float a longer rail or hand guard over it. The same can also be done on midlengths for rifle length or longer hand guards or rails.


There are two standards Commercial Spec and Mil Spec.  Mil Spec is stronger.  They cost about the same.  Get the Mil Spec.  The Buffer tube assembly is comprised of 5 main parts.  The buffer tube, the end plate, the castle nut, the buffer spring and the buffer.  Rifle buffers tubes are long smooth cylinders located aft of the lower receiver.  Pistol tubes look very similar but are shorter, and sometimes have a foam sleeve covering them. Carbine buffers are shorter than rifle tubes and have a rectangular extension running lengthwise on the tube.  In the extension are slots where collapse-able stocks can latch onto in order to adjust the length of pull.  General rule of thumb.  If you have a rifle buffer tube, stick with the rifle buffer and rifle spring. Stick with carbine buffers and springs with carbine tubes.  Most pistol tubes are based on carbine springs and buffers.


Many first time AR buyers will read that, this buffer, or that buffer, will make your gun shoot better and smoother.  Or this buffer spring will be more reliable and reduce the famous AR15 “sproing”.  My stance is that if you are buying a complete AR15, stick with what the manufacturer gives you.  A lot of time and development goes into making your rifle.  Please don’t go off do something silly like changing the timing on your gas system.  Changing the spring or the buffer changes the timing of the gas system.  If you know what you are doing you can fine tune your system to exactly how you want it.  If you are unsure what you are doing, don’t do it.  Changing the timing can adversely affect how your AR cycles. If you do it incorrectly you can induce at out of headches and failures.  You can get failure to feed (FTF), failure to eject (FTE), double feeds, and failure to lock back the bolt at the end of the magazine. There’s lots that can go wrong.  Nothing catastrophic mind you, but a headache nevertheless.

In semi automatic fire, changing buffers and springs does very little for felt recoil.  You really have to have a good feel for your gun and a lot of trigger time to be able to feel the difference in recoil impulse between a H buffer and carbine buffer, its really not substantial.  For a beginner, stick with what your builder put in there, if you building, start with the standard rifle buffer or carbine buffer. Play with the timing later if you like, after you have a few range sessions and more trigger time under you belt.  Its easy to do and cheap too, just please do it later.


For someone just starting out with an AR, I would really recommend that you just get started with a standard mil-Spec type trigger. There are a myriad of choices out there from 2 stage to fast single stage competition types to fully adjustable models for long range competition. To me a good mil-spec type trigger is good for shots up to 200 yards. Beyond that, I feel the need for a more refined trigger and look for 2 stage triggers. I’ve shot with shooters that do amazing things with a standard trigger all the way to 400 yards, but for me I like a good two stage for those distances. If you are going for a precision build or looking to shoot tiny, tiny groups, a light 2 stage trigger has many advantages. First and foremost being the 2nd stage. It allows you to know exactly when and where the trigger will break. Some shooters will prefer a single stage, but most use 2 stagers for precision work. One thing most people don’t know is that a 2 stage trigger will feel just like a single stage if you pull it hard and fast. For close quarter or speed shooting, 2 stagers feels just like a standard single stage trigger.

If you are not sure exactly what you want, just stick with the standard mil-spec trigger. Once you get a lot of trigger time under your belt, you can then re-evaluate your needs. Most people will find that the standard trigger works for them. Some will find that they need something more. As a first timer, don’t upgrade until you’ve got a good reason too, and don’t rush out to put in an expensive aftermarket trigger your first time out. If you can become proficient with a standard mil-spec trigger, you will be a better shooter overall. Also if you train on a standard trigger, it would be easy to pickup any standard AR and shoot well with it too.


As a first time buyer, I would really recommend you getting just the basics your first time out. Get you hands on your AR, some good magazines, and lots of ammo, and then go shoot it. Shoot it a lot. Have a lot of fun with it. Learn to use your iron sights. Learn the ergonomics.

After a little range time, figure out what you need and what you want, and then upgrade it. One of the biggest mistakes that I’ve personally made, is that I bought a lot of upgrades for my AR all at once. I eventually decided that I didn’t want or need most of them and changed them back. In hindsight, I just should have upgraded slowly piece by piece, one range trip at a time until I found exactly what I wanted. All I would recommend is a nice sling, plenty of magazines and ammo, and a shooting buddy or two. Aftermarket triggers, optics, lights, and lasers all have their place, but when starting out, please just take it slow. Learn the basics on your AR. Understand how to use the iron sights and manipulate the ergonomics. Then make changes to suit your personal needs and tastes.

I could easily write a 300+ page book on all the different type of accessories, but honestly the market is constant evolving and this primer would become dated quickly. Just remember to balance your wants and needs, with weight, cost, and utility.


Why isn’t X,Y Z brand good enough? Why are they so much cheaper than Colt, BCM, LMT, or Daniel Defense (etcetera)?  Why does everyone keep recommending brand A,B,C? What you are paying for is intangible, and mostly invisible. You are paying for quality. These brands are what I would consider service grade ARs. These companies (Colt, BCM, DD, LMT) make guns that satisfy my minimum requirements for overall quality for a work gun. I am paying for higher quality components, testing of materials used, and tighter quality controls. I am paying for a company with a track record of NOT cutting corners and experience building quality rifles. For a range gun, I would like 100% reliability but, when I’m in a gun fight, I demand 100%. That being said, nothing is 100% perfect. But at least with these builders/manufacturers they are much less likely to fail when put to hard use. I am not saying that your Vulcan, Blackthorne, Stag, DPMS, Delton, Olympic, Bushmaster, Spike’s, PSA is an unreliable POS. I am saying that Colt / BCM / DD / LMT are less likely to have a stoppage.

That being said, if I had Brand XXXXXX (any make or model) that I plan to use for work, or HD/SD, I would put at least 1000 rounds through it first. I would test it out with a variety of different types of ammo and test out all my magazines. I need to ensure that positively, definitively my AR is reliable and good to go, no matter what make or model I have.  Please don’t just go out and buy a firearm, any firearm, and some hollow points and then throw it in the safe, thinking you are now safe and good to go.  Test, verify and re-test.  The beautiful thing is, testing is fun.


Expect that most lower priced, brand new ARs will start at about $600. Service grade ARs are a bit more starting around the $1000 mark. If you have the time and patience, search the equipment exchanges on various gun boards, wait for sales, get into a group buy or two, and buy your AR one piece at a time. If you aren’t adverse to buying used parts you can save even more. I would not recommend buying a used lower parts kit since they are cheap new. Just suck it up and buy a new one. Delton, DPMS, Olympic, Bushmaster, Spike’s, Palmetto State Armory all make decent quality ARs. From my past research but no personal experience, I would stay away from Vulcan and Blackthorne. I would also shy away from small boutique brands that no one has ever heard of. Remember Google is your friend, use it. Research any complaints with any particular brand or model you are interested in, and also do a quick search of that brand’s warranty and customer service. Do take your time. Do your own research, Do not buy on impulse. Pick a few models that appeal to you and post up your questions and ask for opinions. You will find many helpful people out there that will steer you in the right direction!

Hope you found this guide informative, I welcome any comments and criticisms that you may have.

Digiprove sealCopyright secured by Digiprove © 2012
Acknowledgements: Richard Jung A.K.A. "Agent Tikki"

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24 Responses to AR15 Primer – A Beginner’s Guide to “America’s Rifle”

  1. 702 April 16, 2012 at 2:14 pm #

    I’d like to thank Agent Tikki for sharing this information with the readers of I originally found this writeup posted on a gun forum and asked if he would be interested in publishing it here. Although it’s quite the long read, it’s full of answers to a ton of the kinds of questions I receive regularly from those considering AR builds or purchases.

    This invaluable info can save you a lot of headaches and speed up the AR platform learning curve.

  2. dale s April 17, 2012 at 10:29 am #

    Very good stuff , Thank You!

  3. grim333 April 17, 2012 at 7:13 pm #

    As a newbie to the AR, this is very helpful, thanks.

  4. sharxbyte April 17, 2012 at 8:34 pm #

    Good read! I learned :)

    A couple spelling errors but no one’s perfect ;)

  5. shooterdude April 19, 2012 at 12:28 pm #

    What a great guide, I wish I had read this when I was getting into ARs

  6. Agent Tikki April 21, 2012 at 8:15 am #

    Thank you for all the kind words guys! Now that you are up to speed, what have your decided on getting! :D

  7. mpribe April 25, 2012 at 8:19 am #

    Thanks for the great guide. I am looking to be a first-time AR buyer, and want a gun that I can use in a wide variety of scenarios. One common piece of advice I read for first-time buyers is to just get the basics – get a 5.56 rifle and don’t go for any of the more exotic calibers your first time out. From all my research though, and not coming from a military background, I am much more interested in a caliber like 6.8 SPC than I am in 5.56. It seems to me that 6.8 would be a better all-around cartridge for medium-long-ish range shooting, hunting, and in a SHTF/self defense situation. I just don’t see why I should spend $1000 or more on a rifle now if I’m just going to go out and spend $2000 or more on another one later. Would it really be so bad to skip the 5.56 rifle and go right for a 6.8? If not, are there any manufacturers out there that I should consider besides LWRC?

  8. jlanzijr May 6, 2012 at 8:59 am #

    I have been considering to purchase an AR for quite soom time. (I fell in love with the M-16 back in basic traing in 1971).

    This article was VERY informative and gives me the information I need to make an informative decision on available options.

    Thank you

  9. Codie May 7, 2012 at 9:53 pm #

    This is a great article, extremely informative. Thank you

  10. Agent Tikki May 26, 2012 at 10:11 pm #


    As I’ve state before, the first thing you really need to do is figure out what you need, and what you want before trying to figure out what to buy. Its really seems that you’ve put in some thought, and I commend you for that. When buying a rifle I usually figure out what ranges I plan to use it for and what types of shooting I plan to do. Then I figure out what the best caliber would be to fit my needs. I mean I don’t want to go rabbit hunting with a .308, nor do I want to use a 5.56 on a moose. Lastly I figure out what kind of gun to get that will do the job.

    I think that a lot of people will recommend that you start with .223/5.56 if only because of the cheaper ammo costs. Tho you can get very good precision from an AR15, but it is by design for use with higher rates of fire than your traditional precision guns (read bolt action/single shot). With cheaper plinking ammo running in the low 20 cents a round range, its much more affordable to run it hard and fast. It is not uncommon to go through 1000 rounds per day participating in carbine courses or running practical type shooting events. I can only shudder to think of the ammo costs for running a 6.8 spc through a carbine, a 3 day Larry Vicker’s course will have me getting a second mortgage! (I kid) I can take my 16″ carbine and take it to class with me go through 1000 rounds through it, then take it out to the range and practice shooting 300 to 400 yards free had with the same setup. It’s pretty amazingly flexible.

    Now if you are looking at a dedicated hunting rifle, and will only use it for that purpose, I think a 6.8 spc is an amazing round. Though ballistically I don’t think is does so well at intermediate distance. I’d recommend looking into 6.5 Grendel or .264 lbc for intermediate ranges hunting that can also handle long distance precision shooting. Either way, I probably wouldn’t use either for practical shooting, or running and gunning just because of the price of ammo.

    I have a few suggestions for you that may help you make up your mind.
    1) Get a 223/5.56 first. Buy a 6.8 upper later. This way you can both calibers with out having to buy 2 whole guns! Win Win.
    2) Get a .223/5.56 first, buy a complete 6.8 spc upper later, and sell your .223/5.56 upper if you don’t like it, might lose a bit of money but at least you can shoot the .223/5.56 fer a bit and make up your mind.
    3) Get a complete 6.8 spc AR15, then buy a .223/5.56 upper later.
    4) Get your complete 6.8 spc AR15 and be happy with it.

    Either way, its ultimately your choice. I think that you have thought it through and chose the right caliber for the job. Its not absolutely necessary to start with 5.56, though I do reccommend that most people do. Plan your AR and build it your way! The possibilities are almost endless! Good luck with you build!

  11. slwize June 1, 2012 at 9:48 am #

    I’m new to the AR’s and this article is just what I’ve been looking for to help me make a more informed decision when buying one. No Nonsense and straight to the point info. Thank you Agent Tikki for the information!

  12. Malamute August 22, 2012 at 3:18 pm #

    I am new to this site and just finished your article. It was very informative. Thank you. I would be intrested in reading more from you.

  13. suicyco September 9, 2012 at 7:19 am #

    Very nice read. I started out with a DD m4 v5. I did a lot of research myself before this purchase. After reading this article I am releived that I used basically the same crteria that you suggest for my selection. The only add-on I have purchased so far is a trijicon ta31h which I got brand new for a SCREAMING deal. Considering the rmr add on sight for cqc. I also purchased an Armalite ar-10t for a dual application rifle, mainly hunting, but with the capability of using in an unexpected situation if neccasary. I am considering an EOtech HWS because I cannot afford another really expensive scope for the .308 as they get exponentially more expensive as you move up in caliber I have noticed. Any recommendations for a good scope? I am now considering another ar-15. decided against the piston because of the proprietary parts issue. I am considering BCM,Rock River, or LMT, in that order.

  14. mkraptor September 14, 2012 at 8:48 am #

    This article has to be the most well thought out piece ever written on an AR15 beginners guide platform. I was pretty sure I was going to be lost in all of the gun jargon, but to my amazement it was written simplistically. I am brand new to the AR15 world and I have stopped myself dead in my tracks from buying a rifle that I would not have been happy with because of this article. Parts of this article you can use to other rifles as well. Take for instance the barrel types and contours. That information will help with any rifle choice. I feel like I am now not a beginner at AR15 (even though I do not own one), but I feel I am in the intermediate phase when it comes to knowledge. Thank you for the article. I definitely push this article on my friends, whether they know it all or not, because I am sure they will learn something.

  15. Ronin October 1, 2012 at 5:18 pm #

    This proves you don’t always have to give away items to please the guys in the field… Excellently written articles are good for the new shooters and excellent reviews for the older guys… After all knowledge is the best gift of all… Keep up the good work guys… :-)

    • X702 October 1, 2012 at 10:04 pm #

      Thank you Ronin.

  16. AnEvilCanofWD40 December 2, 2012 at 3:13 pm #

    Excellent write up and information. Now I don’t waste anyone’s time or look like a noob asking questions that were just answered here. Thanks to the site for reposting! I’ll be researching more about the gas piston conversion :)

  17. Aaron January 17, 2015 at 7:51 am #

    EXCELLENT article, Thank you for posting. I spent 10 years active Army Special Forces. I instructed and worked as a small arms instructor at 1SWTG(A) and at times an armorer. I’d be happy to do a peer review of any articles you publish in the future.

    Take care,


  18. bryce hoover March 16, 2015 at 10:22 am #

    great info, thanks! learned a lot.

  19. Jim Sullivan April 23, 2016 at 8:48 am #

    Just want to say thanks for a great easy read and general assessment. I too am new to getting serious into obtaining an AR weapon. Answered a lot of questions and made me aware of even more. You have made it clear the need to look into this area slowly and educate yourself. There is a lot to understand. You wrote this a few years ago but your
    writing on this subject is timeless.

  20. Roger Kilthau August 3, 2016 at 5:52 pm #

    I learned a lot from your articel comparing 5.56/.223 carbines, magazine and super technical advice on the mechanics of an AR15/M4.
    Thank You.

  21. Roger Kilthau August 3, 2016 at 6:04 pm #

    Thank you for helping me to understand the function and mechanics of the AR 15/M4 much better than I thought I knew and helping me to decide which carbine to purchase. That includes Hybrids and magazines.
    Thank You.

  22. Bob A July 29, 2017 at 7:30 am #

    AS of 2017, there are plenty of sub-$1000 ARs that will perform as well as name brand makes in 99% of functional areas. Smith and Wesson, Ruger, Delton do quite well. If you are new to ARs, do not fall into the trap of believing money gets you that much more quality and reliability. There is limit to return on investment. Exotic metals, fluted barrels, unneeded parts such as anti-roll parts for pin crawl out, nickel boron BCGs. Many name brand ARs continue to use chrome lining instead of nitro-carbuerizing treatment in their barrels.
    Still, this is one of the better guides I have seen. I would follow this in a heartbeat with the caveats I mention. Very good article. Bookmark and/or copy the text and study. Last caution: do not fall to peer pressure buy what you need not name brand. Spend what you save of optics, cartridges or even a second AR!


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