I have a new A2 upper. It has consistent failure to feeds (50%+), as well as occassional failure to hold open (10%+) on empty mags, with one RRA lower (RRA two-stage NM trigger) but not with another RRA lower (single-stage trigger with JP 4.5lb springs).
It appears that the bolt carrier group has more drag on the first RRA lower compared to the other lower. It seems that RRA two-stage hammer exerts more upward pressure on the BCG than the regular trigger.
Other uppers shoot/feed fine with both lowers.
This new upper does not have the bottom center of the BCG polished.
Would you recommend that I polish this as a first step to fixing the problem? Or, should I start somewhere else?