Rifle 101: Hammer Forged Barrels Aren’t Always Better

Some readers may be surprised by the results. The US-made barrels are nearly as hard (or harder) than hammer forged, military spec parts from countries that have been doing it for years! How is this possible? The key here appears to be the material the barrels are made of, not the manufacturing process.

Unlike the American CMV barrels, many enthusiasts feel that the hammer forged versions are made of simpler (or at least different) carbon steel, and a few versions at that. By itself, the imported carbon steel appears to be slightly softer than CMV 4140 and 4150. After work hardening via the hammer forging process, the military spec barrels seem to approximately match the American CMV alternatives. All else being equal, hammer forging produces a harder barrel. But all is not equal if the steels used in different parts of the world are, in fact, different – and they are.

This brings us to another consideration. We aren’t getting the full story from the US-made barrels, at least as far as the Green Mountain barrel is concerned. Green Mountain barrels are (mostly) produced using a cold-forming method called button rifling. To add rifling to the barrel, Green Mountain pulls an extremely hard button (with the rifling negative) through the barrel. This button moves steel to create rifling rather than cutting it. Thus, the bore of a button-rifled barrel undergoes work hardening similar to forging. Mel64D tested the outside of the barrels, capturing the work-hardended surface of the forged parts, but not the hardened bore of the button-rifled tubes. We should limit conjecture here, but it’s reasonable to say that the most important parts (the bores) of the CMV barrels may actually be even harder than the values shared here.

Now observant readers have probably noticed that I have yet to mention additional details like the presence of chrome lining or nitride finishes. For this discussion, we are going to ignore such enhancements. Generally speaking, the process to chrome line a barrel is the same, regardless of origin or manufacturing style. Chrome lining results in a harder bore, but if the underlying steel is soft, its advantages are diminished. None of the barrels in Mel64D’s test were nitrided, so the advantages of the process are fairly irrelevant at the moment.

While it is always possible that Mel64D’s test setup was improperly calibrated, his methodology looks to be sound. It’s also fair to question whether hardness is everything when it comes to barrel toughness. There’s no doubt that hardness is touted as an advantage enjoyed by hammer forging and Mel64D’s video isn’t intended to dispute that claim. Rather, his findings seem to confirm that we often get far too wrapped up in how barrels are made, sometimes forgetting that the materials that go into them are equally important.