Cause: likely a stuck wad, base wad, cleaning patch, wasp nest, etc. hung up in the forcing cone that acted as a momentary but effective barrier to the next charge of shot coming out. 3" shells in 2 3/4" chambers cause a pressure spike to one degree or another when its case mouth extends past the chamber upon discharge causing the shot charge/wad to have to elbow its way past with a little more difficulty than normal. The increase in pressure, such as it is, is thence confined to the chamber, and typically won't actually bulge the barrel ahead of the chamber. I've never heard of a 3" in 2 3/4" (or 2 3/4" in 2 1/2", etc.) actually causing a bulge. Bulges happen when shot charges encounter obstructions, and it doesn't take much of an obstruction.
As for said bulge being back so far in the barrel- yes it's "more dangerous" than a bulge close to the muzzle where internal pressure has tapered off dramatically behind the escaping shot charge. Will it blow next time it's fired? Maybe, or maybe it'll go the rest of your natural life without blowing. No way to predict it. How lucky do you feel?
What's a "Ruko" by the way? Is that short for Miroku?
Thanks for the info, I’ll let the guy know that it’s a bad idea to use the barrel.
