Originally Posted by
Duelist
M60 and M240b and M2 and M249 all fire from open bolt (IIRC, part of the design intent is to keep a hot chamber from cooking off a chambered round and to let the chamber air cool during breaks in firing). If the new gun also fires from open bolt, then the heat of the chamber isn’t going to cook the resins of these cases just like the older designs are avoiding cooking off a brass case cartridge, since they aren’t sitting in the chamber waiting to be fired. The rest of the gun can get hot, too, of course, but not anything like the chamber and barrel.
Gunners or assistants are already carrying spare barrels for the machine guns (maybe not so much for the M2). I don’t remember the number, but after X rounds/minutes of fire, when possible, they are supposed to swap barrels to let the hot one cool off. Or if they can’t change during an engagement, afterwards, or after they’ve toasted a barrel with sustained fire.