Take off the barrel and examine the chamber with a good light. See if there's pitting, rust etc. near the mouth of the chamber, or plastic buildup in the chamber itself. If you see any evidence of these things, give the chamber a thorough cleaning with a new barrel brush wrapped in 4/0 steel wool with a plastic dissolving solvent. Or you could use part of a copper Chore Boy pad or the like set into a split dowel.
With a clean chamber, try a couple different brands of ammo and see if they work better. Sometimes a good cleaning and a switch in ammo brands are all it takes.
It may be that things are so bad you'll need to hone the chamber. A small brake cylinder hone in a low speed eletric drill using ATF as cutting oil might do it. It could be you'll want to leave stuff like this to a gunsmith if you aren't confident honing your own chamber. Remember, it's easier and cheaper to remove metal than it is to put it back. Go slow and get your 'swirlies' right- and confined to the chamber.
Beyond that I have no simple solutions to offer- it's gunsmith time after that as far as I can tell.
lpl/nc
