Today I received, by email, an interesting paper – from 1968 – which discusses DOD testing regarding materials to be used in the making of barrels for small arms. Before I go too far, we have to understand what a “small arm” is. To the military, this can be something which is quite a bit larger than what a civilian might encounter at a gun store or shooting range. This report was done at the request of the Air Force, which was interested in improved materials for minigun barrels up to 30mm. However, if a material is found to be suitable for use as a 30mm minigun barrel (and the miniguns referenced in this paper can fire 100 rounds per second through their six rotating barrels), it will probably be suitable for use in a semi-automatic rifle firing 5.56mm or 7.62mm ammunition.
The paper is difficult to read, for it appears to be a copy of a copy of a copy. However, what is legible is pretty interesting, if you’re a gun buff like me. If you want to learn technical stuff about barrels and how they wear, read the first few pages.
Some interesting highlights include:
– Titanium, and titanium alloys, displayed significant wear after a single round was fired.
– Chrome moly vanadium barrels which were chrome lined offer greater wear resistance over barrels that were nitrided (also known as Melonite, Tenifer, etc). This is relevant to folks who are considering a new AR-15 upper or barrel – nitriding comes at a lower price and does extend barrel life compared to a bare steel barrel, but it’s not the equal of chrome lining when considered from a barrel life standpoint. It may offer other benefits, such as a slight increase in accuracy, but that wasn’t part of the study. As we see in this study, nitrided CMV barrels, when used in a machine gun firing 200 rounds per minute, will last up to 30,000 rounds, while bare steel barrels lasted on average under 10,000 rounds.
– Chrome moly vanadium barrels with Stellite 21 liners that were then chrome lined set the standard for wear resistance.
Another study to read if you want to learn about barrel material, rate of fire, and barrel contour as they relate to machine guns – in this case, M60s and .30 caliber Brownings – is this 1974 paper. The major lesson to be learned is one that most folks already know – lighter barrels, though nice from a weight standpoint, will die faster than heavy barrels when shot for extended periods of time. We also see this in a destructive test of the (heavy barrel) M4A1 versus the (lighter barrel profile) M16A2 – although both barrels failed at approximately 1600F, it took longer for the M4A1 to reach that temperature.
And finally, if you’re an environmentalist who loves cannons, there’ something for you, too.