Re: Bulged Barrel?
The actual cause of a bulged barrel is often misunderstood. It is heat. When the bullet begins to move, it rapidly picks up a lot of kinetic energy. When the bullet is stopped abruptly, that energy is dumped in the form of heat. That heat softens the steel of the barrel and the normal pressure bulges or breaks the softened steel.
If the bullet is not stopped, or slows to a stop, the energy dump is not as abrupt and the heat has a chance to dissipate. That is the case with a soft material in the barrel (peanut butter?) or with something like rainwater, which does not slow the bullet significantly. But if the front bullet is at the rear, so the second bullet is touching it, the second will not be stopped, and the two bullets will exit as one, at effectively double the mass. The pressure will be higher than normal, but the the barrel will not bulge.
Also, if a bullet is stuck in the barrel and a round without a bullet is fired, the powder gas alone does not have enough kinetic energy and is not stopped abruptly enough to cause a bulge. In fact (dirty little gunsmith secret) a common way of removing barrel obstructions like broken bore snakes is to use a half charge of powder without a bullet and simply shoot them out.