There are few parts of an AR that are as important as the bolt carrier group. While the standard Mil-Spec bolt carrier does its job well and has for decades, new improvements in technology and materials have come along and revolutionized the design. When looking at the Best Bolt Carrier Group to use for any AR-15, there a number of factors one must consider. Like many aftermarket pieces for ARs, much depends on what the intended purpose of the weapon is, what sort of budget you have to work with, firing frequency, and of course aesthetic appeal. However, before we delve into the finer points, lets first understand what a bolt carrier group is and what sorts of duties it performs.