I ran in to the same issue with my groups. I shoot a single shot rifled barrel. So feeding and the like was not the issue. I actually found this on another site and while I've only tried 3 of the brands the Remington Accu tips gave me the best groups 2.5 inch. Winchester Platinum...bad
Winchester Partition...bad
Hastings Laser Accurate..Had some good groups, and some flyers.
Lightfeilds..great at 50, very poor at 100 yards.
Remington Copper solids..pretty good!
Remingto Accu-Tips..Very good.

Hope it helps