I converted my 12 and 16 gauge Mec's to 2.5 and don't bother even loading 2.75 shells I just shoot 2.5s in the 2.75 shotguns. Bismuth loads get roll crimped so we can tell, even in the dark if I have waterfowl loads.. I did convert an old 20ga MEC to load 2.75 10ga for my old sxs. I couldn't do 2 7/8 without making drastic changes but 2 3/4 work just fine.

After the first shot the rest are just noise.