Amazing how much 'change' happens with component variations - different wads, different powders, different projectiles. My .58 double printed 2 1/2" vertical separation first couple times out to the range - changing patch thickness and ball size - larger ball and heavier patches & more powder removed the vertical dispersion and both tubes now shoot to the same point of aim at 50 yards.

Pretty much the same happened to my 12 bore smooth-rifle. changing wads & powder charges moved the barrels together perfectly, but it was a fairly narrow breeched gun. Many shotguns have too much separation at the breeches, but heavier charges can separate the impacts. This is where black powder charges can come in handy, due to the much heavier recoil for any given velocity over smokeless loads.