Seems as though you either are confused by all the advice, or are waiting to get the answer you want.
I get that most are saying the gun is not suitable for any long term (or at all) use of hi-pressure loads, which yours seem to be, with that much Bullseye - (Scary as H.. to me, actually). As far as fixing looseness, take it to a good gunsmith and find out if the problem is locking bolt wear, pin wear, stretch, or......
No insult intended. You asked for an answer, my opinion.

Dumb, but learning...Prof Em, BSc(ME), CAE (FYI)