FWIW, I went to a two piece scope mount. MUCH better! In regards to the ammo loading...my frustrations seem to have been a brand/type issue. I'm neither endorsing nor discouraging the use of any of the following.....
Federal power shok 3" 1 1/4 oz. magnum - the source of my magazine loading frustration. The only differences I can see between these rounds and those that loaded with no problems are
a. It's slightly longer. 1/16 to 1/8"
b. The brass butt cap is 3/16" shorter than the other two. I believe this allowed the cap on the slug being loaded second to hang up on it's edge. With the other two rounds the caps were long enough so the round on top didn't slide across the edge and hang up.
Rounds that loaded with no problems...
Remington Slugger 3" 1 oz. magnum
Remington Premier Copper Solid Hollow point 3" 1 oz. magnum
Hope this saves someone the frustration
I experienced.