What i do find helps a lot with consistency is having the butt adjusted so the natural point of aim is on target. And I pretty much do this for every one around a course. Courtesy of an AJP knob. Coincidentally, my sitting position puts the bore line roughly central to the butt so any recoil tends to come straight back and not up.
That said, Mr Murphy and others swear by a stock rubber butt.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep