David- Believe it or not the way to get a smooth bore barrel regulated to point of aim is to bend the barrel, I'm totally serious, usually gunsmiths
don't perform this proceedure in front of the owners for obvious reasons
they either chuck up the barrel in a lathe or place it between a couple of
peices of 4x4 and proceed to whack it with a large rubber mallet, I'd recommend calling a couple of smiths, it's a very easy job but not one
for a beginner unless you're somewhat adventurous.
fredj