"It's a post-assembly heat treat"

Phrases like these are what anyone worth their weight in detents would call "Fudd Lore." The general logical thread of such wisdom is that the steel of a barrel needs to get pounded through a live-fire cycle of heating and cooling to somehow "finalize" or "reset" the heat treat that was (presumably) conducted by the manufacturer when the barrel was produced. The end-goal of this process is the temper the barrel steel and improve accuracy through mystical means like somehow "aligning the bore to the harmonics of the barrel." Like most Fudd Lore, this checks out if you are otherwise uninitiated. This piece of lore, however, is particularly irritating because it nearly reaches the levels of other greats like "revolvers don't jam" and ".45 ACP: The Manstopper" due to it's shared distribution network. Since Militiaworks manufactures AR-15s, that application will be the primary focus of this article.

Grounding our accuracy

Despite what the guy in the gun shop told you, every weapon platform is not meant for or capable of shooting a .25 MOA group with cheap Russian loads. Maybe they are a "true marksman", but it would be wise not to make that your benchmark for accuracy. There ARE absolute tack drivers that can punch a ragged hole 200 yards and beyond with the right loads, conditions, and (most importantly) a capable shooter. You may be that shooter, but an off-the-rack AR-15 can generally be expected to shoot 2-4 MOA with factory-grade ammunition (Winchester white box, PMC, etc.). Ballistic Advantage, and subsequently Militiaworks, guarantee sub-MOA groups with match grade ammunition, which is great for the platform but far from a common spec. There are many quality barrels out there, but it is important to keep the scope of our expectations of performance within the realm of possibility.

Smooth is... smooth

Much of the relevant data to any "break-in" procedure is a result of the materials and processes used to produce it. As we discussed in last week's article, there are three primary methods of producing barrels today: button rifling/gauging, cold-hammer forging, and traditional cutting. Only two of these, button rifling and traditional cutting, can result in a bore that requires a break-in. In the case of button rifling, quality barrel manufacturers follow the cutting tool with a finishing tool that deburrs the edges of the lands and smooths the surfaces within the bore so that they are clean before the surface finish is applied. Typically, break-ins are effective for one category of barrels: those made of softer materials (i.e. 416R stainless steel) with traditional-cut rifling. Even in this case, their is no one-size solution. The manufacturer will prescribe a process that yields the best results for their barrel and you should definitely follow it.

The reason for such processes is that there may be small rough spots, burrs, or other imperfections resulting from the cutting of the rifling within the bore. In precision applications, these imperfections can cause small deformations on the soft jacket of the projectile, which may lead to noticeable deviations in point of impact at longer ranges. Usually, these processes sending a few rounds through the barrel, cleaning the bore, and repeating a few times. The shooting and cleaning cycles can smooth rough patches and displace small burrs, thus reducing the variability of the barrel's ballistic dynamics. Unlike what the Fudd lore may suggest, this is a simple friction polishing process and has nothing to do with heat buildup.