I made a brass trade here for some .45 Colt brass. I got the package, and like half of them are REM-UMC nickel plated brass. I went to size them, and my Lee#11 shellholder does not fit them. It fit all the other brass, just not these ones. The nearest shellholder that sort of fit them I had was a Lee #5 , which is for my .303 Brit reloads. And it doesn't fit them well, just barely works, still really tight to get it in the shellholder. When I looked closer at the brass, it doesn't have the groove cut in it just above the rim, like the normal .45 Colt brass. Pulled out my .454 Casull pistol, and they seemed to fit in the cylinder ok, so I'm still going to reload them.
But is there something about REM-UMC brass I've never heard of?