If it really is "fine for the first 100 rounds or so", that immediately suggests chamber cleaning(to me) as suggested above. The chamber(s) getting dirty is the likely thing that would progress in that manner. Let us know if chamber cleaning helps. Be sure to use a chamber brush. A bore brush is too small and too soft to clean the chamber. If you can't find a chamber brush for your gauge, get a brush for one or two gauges larger.

> Jim Legg <