I have a rra direct impingement ar pistol. ..went to go put some rounds down the pipe yesterday and ran into an issue.     It shot 3 0r 4 fine. But then went single shot...  it would eject and feed a new round but the hammer was failing to reset.

Is the gas port too small on these?     Are there known issues?      I did some research but was mostly getting info for their pds pistols. ..

I don't own one so maybe I'm wrong... Your problem does not sound like a port/gas or other cycling issue, sounds like the hammer is not catching the disconnector. Try this, take the upper off, decock the hammer and hold the trigger fully to the rear, now, try and reset the hammer. did the disconnector grab and hold the hammer or does holding back the trigger keep it from catching?

I was thinking something along problems with your FCG as well, however being that I am still rather new to the AR platform I have no further info to offer other than to reiterate that it does not sound at least at this point like a port/gas issue.

Yeah sounds FCG related to me as well. I don't know the RRA line up... Heck I'm not even sure what a "direct gas pistol" is... I'm assuming OP means DI. On DI AR's pistol or not the hammer is reset about half way thru the rearward movement of the BCG, it's impossible for the BCG to travel back far enough to eject and feed and not reset the hammer.... the hammer has to be following the bolt instead of being captured by the disconnector.

Yes.  DI.  Not piston.     Most of the info I have found is for the pds pistol from rock river. ....

Problem fixed.    It was the trigger.     When I did the trigger job I cut the secondary sear on a slightly negative angle and it wasn't hooking.