I apologize for commenting again but wonder what kind of a lesson we're providing by the above examples: nothing happens with 20ga and mud, kerboom? I wouldn't think of cutting my leg with a chainsaw to demonstrate if my first aid kit was any good!
Would anyone on this forum like to take 100 different 12 ga shotguns drop a 20 ga shell in and then put in a 12 ga shell and pull the trigger? One incident or even two or three incidents statistically tells you
nothing . That's one of the reasons I've never agreed with the conclusions of Sherman Bell's damascus vs. fluid steel testing as it was far too limited(sample size wise)in scope to have any real validity
Jim