Miller, although Bell does not tell us in his article, I'm guessing that when he fired 3" magnum hulls in Armbrust's 2 1/2" pressure barrel, those unfired hulls likely extended into the cone. There was an increase of about 700 psi--from 10,953 to 11,665--from the 2 3/4" chamber to the 2 1/2" chamber using those 3" shells. But I agree with you that shoving an unfired shell into the cone is likely to be risky business.