If you are making 7.7 brass out of 06 brass just don't tighten your sizing die down - let it leave the case a bit long. O6 brass will awlays bulge at the base as it is smaller than 7.7 brass. Fire you brass till you see a faint white line just above the base. If you stop there you are alrigh but the next loading most likely the head will seperate. As someone has already said the chamberrs on most military weapons are oversize to take care of dirty or oversize ammo. They are safe to shoot. Don't wast your money on a "gunsmith" to protect himself he will tell you not to fire your rifle.l roy