Bolt Carrier Groups / Parts

Bolt Carrier Group’s (BCG’s) are as important if not more so than the barrel selection. There are several things to consider about BCGs. They consist of two parts, the bolt itself and the carrier, which contains it. Bolts need to be manufacturer using hardened Carpenter 158 steel or S7 steel as they need to sustain high pressures repeatedly and reliably. Additionally bolts need to be MPI (Magnetic Particle Inspected), Shot Peened and HPT (High Pressure Test) tested. The bolt is the most likely item to fail and therefore a high quality bolt is imperative. As for the carrier there are two primary considerations, first is the fact that the gas key must be properly staked in a quality bolt carrier and second the finish of the bolt carrier will determine its lubricity and how well it operates as well as ease of clean up. Some bolt carriers are chrome lined and may be preferred by certain shooters, although we have found that certain carriers that have a black nitride process applied function just as well. Different carriers have profiles, which are designed to reduce friction or weight as it cycles through the receiver and these are typically preferable as they tend to function more reliably and consistently. Standard carriers have a phosphate finish and are the most difficult to clean but can still be very reliable if they are of high quality. We recommend bolt carriers and bolts which have either a black nitride or nickel boron finishing process applied to them as they are easier to clean and more reliable in general.

Also considering that, as mentioned above, the bolt is the most likely component to fail, we recommend keeping an extra one on hand as you never know when you might need a replacement. This is an especially important consideration if you have a 7.62x39 caliber build in mind. As the casing is larger diameter than standard 5.56x45 NATO case, so the walls on the bolt face are thinner and as such more likely to fail.

Although most bolt carriers are designed to work in a standard gas impingent system, there are bolt carrier designed to work in a piston system such as Adams Arms provided. There are pro’s and con’s to both designs and such a discussion is beyond the scope of this information provided, its important to note that such options are available for those who choose to utilize a piston system which requires a unique bolt carrier and other parts like a piston gas block and piston rod. Otherwise, bolts are the same for both systems.  As noted above, a high quality bolt should be made of hardened Carpenter 158 steel or S7 steel, and should be properly tested and inspected to ensure that it serves as long as possible without failing.

All the parts we carry here at AR15-supply have been properly tested and inspected. They are all made in the US and meet or exceed all mil-spec standards.