My own shooting with large bores has shown better accuracy when shooting "dirty". That is, my groups are more consistant and velocity readings more consistant when shot without cleaning or swabbing between shots or within groups of shots.
: If I understood correctly, anything over 80gr. opens up the groups by crossing the barrels. This is unfortunate.
: Have you shot black powder in it? Pyrodex is NOT black powder, and neither is T-7.
: Both of these BP replacements foul very little compared to real BP, yet I have never had to clean between shots or between groups with real BP, which is the only powder I use.
: Try to find some 2F GOEX, Swiss or Sheutzen black powder and let us know how that shoots. As well, you might try GOEX black powder in 1F grind. 1F is generally for large bores and black powder ctgs. Some guns prefer it. Mine preferred 2F for heavy charges. With 82gr., I could use 3F and receive 1,200fps, but any more would burn patches, so I had to use 2F for more velocity.(69 cal.)
: A good lube in large bores is Stumpy's Moose Snot. 2oxz. beeswax, 8oz castor oil, 1-1/2oz murphy's oil soap. The oil soap is necessary to cmbine beeswax and castor oil, and is added when the castor and beeswax are hot and well stirred. Add the Murphy's then whip the rusulting lube into a froth, then pour off into containers. I use old bullet boxes.
: Another good lube is Lehigh Valley lube from www.trackofthewolf,com Another good lube is 50/50 mix of alcohol and murphy's oil soap, apparently.