I have an old 110 that was a 243 Win. I also had a 300 WSM barrel laying around and a magnum boltface. I turned and threaded the WSM barrel to "small shank" specs and installed the boltface. The WSM cases were too fat for the attached mag box, so I opened up the feed lips a bit w/ a dremel tool. I let the follower alone. Now the top round feeds fine, when it is ejected, rounds 2 & 3 pop out of the mag box.
OK, I took too much off of the left or right side of the mag box (maybe both). How do I fix this?? What parts do I need to make an older 110 SA feed a WSM case??