: Do the barrels cross further with more powder?
: Do they shoot a smaller overall group with less powder?
: My buddy uses only 120gr. of 2F GOEX BP in his .75 for moose and gets one shot kills every time. More powder really isn't needed although some guns shoot better with more. His gun is a single, of course and he never needed the fast second shot, although he does carry paper ctgs. that can be loaded in 10 seconds in his gun, 8 seconds in my 14 bore. Nether of these guns need more powder than 120gr. although I routinely used 165gr. in mine.
; Try reducing the charge to 110gr. of Swiss. That should be equivalent to 120gr. GOEX, give sufficient power for any game you are likely to shoot in North America, including the big bears (not black bears) and may shoot closer together. It may also bring the barrels closer together.
: If it doens't, the only suggestion is to send it back to Italy for re-regulating, or to sight for one or the other barrel and use that for your first shot, knowing where the other hits. Many of the doubles of the 19th century didn't shoot together and the owners learned to shoot them accurately by holding accordingly.
: I would suggest your double should hold in 3" or less at 50 yards, firing alternatively, lefts and rights or visa-vis. ome guys use T7 or Pyrodex in them, however I trust only real black powder.
: The crowns of the barrels generally need to be rounded to allow loading sufficiently tight combinations as to give the requisite accuracy. A piece of 320 grit emery under your thumb, after a sharp taper (about 60 degrees) is cut with a chamfer tool, will give you the crown needed. This prevents cutting the patch upon seating the ball in the muzzle, prior to shoving it onto the charge.