Shotgun Bore Burnishing.
This applies to all shotgun bores other than chromed bores, all shotgun bores are polished but not burnished, burnishing removes all the scratches from shotgun bores left by polishing with abrasives.
Burnishing actually closes the pores in metal and leaves the metal surface very slick, it will make almost any shotgun more consistent in patterning and point of impact.
It reduces substantially plastic fouling left in shotgun bores from plastic wads, which reduces pattern consistency.
Burnishing is really simple to do but is very time consuming, when done properly it can be very rewarding in benefit of pattern density and consistency.
To burnish a shotgun bore all you need is:
(1) A piece of dowel rod the length of the barrel.
(2) An electric drill.
(3) 0000 steel wool which is my favorite.
Take the dowel rod and make a few nicks in the end that you will run through the bore just enough to grab the steel woool, wind the steel wool around the dowel rod like a q-tip just enough so that it will pass through the bore of barrel while being spun by the drill, next just chuck the rod in the drill and start burnishing, run the whole rod back and forth the entire bore for about an hour.
If the bore is rough from rust a little shot of wd-40 on the steel wool will help.
I have used this method on all my shotguns and results are always the same extremely bright bores and consistent shooters.