I don't believe it was the resizing of the brass. I compared the rim cut on the offending gun to another antique, just not as old and the was a very small difference. One gun was made in 1922 and the other in 1905, both English/Scot made. The 1905 was tight by the smallest amount. I polished the rim cut with a dremel stone and now shells drop in completely.

This ain't a dress rehearsal , Don't Let the Old Man IN