I had one receiver that was slightly warped in the rear stock block area. The cut outs for the bolt carrier insertion were just a tad too tight also. I opened them up with a file - a little bit at a time, file and fit, file and fit, etc. until it went in.
The corners of those cut outs can also cause the bolt carrier to lock up on full retraction. I messed with it quite a while and it got better but still did it occasionally. I put in a reoil buffer on the recoil spring which limited the rear travel some. No problems since then.
Look for slight malformations on the corners of those frame cut outs where you insert the bolt carrier. If you have had to rap the bolt carrier with a hammer, you will have slightly burred the corner that is hanging. Smooth it out some.
Another way of doing it is to slightly round the corners on the slots on the bolt carrier where it rides in the top rail.
Don't go overboard removing the metal. Too much and the bolt carrier will jump out almost every time it is retracted. If that happens, you will HAVE to use the recoil buffer to limit the bolt carrier travel.
Good Luck!