Trainer A felt that extended cyclic fire of blanks could damage a barrel just like extended cyclic fire of standard ball ammo. The reason being that the Blank Firing Adapter on the muzzle will keep the hot gasses inside the barrel causing heat to build and damage to occur.
He's correct.
Machine gun barrels are tough, however, they can fail due to excessive heat generated by live or blank rounds. While I wouldn't worry about failure from a 200 round burst, I wouldn't make it a habit either.
I have never seen a MG barrel fail on any of our guns, including the 249's, however, that is largely due to proper control on the part of the gunner and leaders, and doing proper barrel changes. Whether blank or live, we used the same time standards for barrel changes as prescribed in FM 23-67/8, and if we used our 249's in a sustained fire role, we did barrel changes with those as well.
Remember that the barrel and bolt both must contain the pressure of the round until the gasses are bled off into the gas tube and fed back into the system to unlock the bolt and continue the cycle of function. Metal becomes more pliable as it is heated, and given enough heat, a barrel may not be able to contain the pressure of a round before it is properly bled off. Blanks are perfectly capable of creating that heat over time, just as live rounds.
The only barrel ruptures I can recall were from M4's being used in the automatic rifle role. Those barrels aren't designed for that type of employment, even the heavy barrel mods, and after being fired on auto, they overheated and ruptured. Not good.
Stick with prescribed rates of fire, especially in training, as they are there for a reason.
