Note, that since the introduction of the fold crimp, nearly all British shells "Factory" loaded for the 2½" game gun have been put up in cases longer than 2½". Also note, as has been mentioned here on numerous occasions, several US makers intentionally chambered their guns about 1/8" shorter than the shells they were meant to fire for the purpose of "Improved Performance". In both cases the shells were longer than their chambers, & they were the shells the guns were "Meant To Fire". A thorough understanding of the reasons is far better than blanket statements, which is the purpose of this board.
Miller

Miller/TN
I Didn't Say Everything I Said, Yogi Berra