At one time I had a Parker with 2 5/8 chambers that were " stepped " at the end of the chamber. Also have one with 2 7/8" chambers. I cut shells to fit each gun and that gave me problems keeping the two sizes separated when loading. So I just shoot the 2 3/4 till the ends are ragged, then trim to 2 5/8. Takes less spacer wads and they work great in the longer chambered gun. Might even go to 2 1/2 to get a bit more life out of the expensive 10ga shells. Just a idea.

My brass cases that I shoot in both my 10 ga guns have obviously fired formed to the larger of the two chambers. Now they don't fit in the smaller chamber. William rightly said the reamers of those days and the operators using them just didn't cut everything the same. He's also right saying cutting a little on a lathe would be an easy fix. Except I don't have a lathe.
So my fix is going to be cull out shells that still may fit the smaller chamber and buy some new ones for the larger then segregate my shells. I can't mix them with both guns anymore. I'll just notch the rim on them to tell them apart.
It ought to make an interesting duck/goose hunt when I take both guns out.
Thanks for all your insight.