I have one of the earlier encore models, in the beginning I had very similar results. I tried the 150 gr Pyrodex RS with 250 gr SST and about 4" group at 100 yards was my best group. I ended up going with 120 gr of Pyrodex RS and a 300 gr SST. I ended up having a friend make me some brass adapters to shoot 400 small bore rifle primers and my accuracy definitely improved, but I can't swear that the primer is the key to accuracy. I have heard that the locker pin is an enhancement to the accuracy,but I have my doubts about that as well. Since the scope is mounted to the barrel I don't see reasoning other than taking some slack out of the receiver but I have 2 encores and both are very well made and have a very tight tolerance. My encore did improve but it was more likely removing rough spots in the barrel from machining. All firearms regardless will have machining marks, I would use some JB's or slug your barrel and use some lapping compound. Mine is like fine wine, it gets better with time. I have take several deer at various ranges and it performs as wellas any rifle. I actually prefer my encore over almost all my center fire rifles except for my Sharps Hartford model. The Hornady SST bullet with the sabot that comes with the are tight, but the SST Lowdrag tends to load easier but the shoot very well in mine. Inever could get good groups with T7 in mine, but my son has had great success in hisrifle. My other ML's get good results. Good luck and let us know how it goes.

V/R
Mike