Disclaimer: Again for the sake of simplicity and brevity, I will only be referring to the most common 5.56x45 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 remmington.
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!
What Chambering Should I get?
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. For more information please refer to http://en.wikipedia.org/wiki/5.56%C3%9745mm_NATO
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.
The Heart of any AR is the Barrel and 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 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 go 0-300 yards quite easily. A decent AR with a great barrel should be able to shoot 1 MOA or less in the ideal conditions (bench rested, 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.
What barrel length should I go with?
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).
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.
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. For longer distances (400+ yards) you should consider a heavier and longer projectile, like a 69 gr, 77gr, 80 gr etc. For those bullets, a faster twist rate (1x8 1x9) is needed to stabilize the projectile. Long distance shooting is usually not for your average first time buyer. There are a lot of 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. One added 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.
What twist rate is good for me?
The longer the projectile, the faster the twist is needed in the barrel. Nowadays, the most common rate is 1x9 (one twist per nine inches), which is optimal for stabilizing 55 grain. 1x9 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 1x7. Most milspec barrels are 1x7 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. The optimal projectile is about 75 grain. It should not be used for very short projectiles i.e. 40 and 46 grain projectiles.
The third most common twist is 1x8. 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 1x12 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.
What is a CMV 4150 4140 CHF BFH HP MP CL SS barrel?
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 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 will last a lot longer and be a little easier to clean.
An alternative to chrome lining is ferritic nitrocarburizing (FNC) aka Tennifer and Melonite. So far I am only aware of S&W and LWRC using this process on AR barrels. This process treats the surface of the barrel itself, unlike chroming. It is a case hardening process that infuses carbon and nitrogen into the metal itself. My 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 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 undetectably 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. 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.
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 ditch 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 mag after mag of ammo, 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 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 that 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.
Bolts and BCGs
The bolt is housed within the bolt carrier assembly (BCG). These are the parts that cycle back and forth within the upper receiver every time your fire your AR. When you pull the charging 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.