The Uzi mag, if properly modified, should feed (reasonably) anything.
Make sure the mag block hasn't slipped a little bit. The feed ramp is part of the block, so if it moves up or down even a little bit, it will affect feeding.
As to the accuracy, I've had decent accuracy from most factory loads, but my best accuracy has been with the NATO standard 124gr and heavier rounds. Mine particularly like the 147gr JHPs.