50/70 questions

[Dave951]

I’ve been working with a 400gr and the Lyman 515141. The 400gr is a modified actual 50/70 design where we added a spire point instead of a meplat. The modified bullet drops at 517 and the Lyman at 515. I’ve tried as cast, 516 and sized to 510. The larger sizes give seating problems while the 510 wants to fall out of the case. There is no charnge in grouping. My thoughts there is the rifling is so pronounced that even the 510 bullet has enough material displaced entering the rifling to seal the bore.

So is it possible that the seating depth/wad etc can be the cause? I’m not beyond relining it but would rather not.