Got a CMC Tactical Flat Trigger for my CMMG 9mm pistol.  This is CMC's drop in job.  Nice piece of machining but...having trouble with the trigger reset.  In cycling an empty gun, pull trigger...click...cycle charging handle and click...works great.  Loaded the mag, cycled charging handle, crisp clean trigger break..bang.  It would run two or three rounds then the trigger would not reset.  Hand cycle repeatedly ..ok...then load up and it would run 2 to 10 rounds then.. nada.  It will strip the 9mm from the mag, go into battery, fire, eject shell, load second 9mm but not rest the trigger.

***Please note...the CMC trigger was ...designed for an AR...and they run like a scalded dog.  But I was hoping that I could pull it into the 9mm platform. I'd hate to go back to stock AR trigger  Anybody had any success/problems with this?  Thanks for any help. .

The CMC has a notched hammer - my guess is it is catching on the bolt. Folks who run a traditional AR15 notched hammer have the same problem. Sorry, don't have a fix for you.

I have the same problem.  Seems that if you are running a ramped bolt there is not enough material on the CMC hammer to reliably allow the bolt to push the hammer down far enough to engage the disconnector.  Some folks get lucky I think it is just a combination of how their particular upper/lower combo allows the bolt to contact the hammer sufficiently to reset the hammer.  I love the trigger but it would not run with any of the 3 ramped bolts I have.  Tempted to try a POF trigger as their hammer appears to be more traditional in shape.   If you are not running a ramped bolt I'm not sure what is going on.  All my buddies run ramped bolts or I would have tried to drop a non-ramped bolt in to test.  Best of luck.  Let us know what you find.

Colt-style 9mm ARs work best with hammers that look as close to an original M16 hammer (minus the auto sear hook, of course) as possible.  The face of the hammer seems to be the biggest interface issue, so notched hammers often generate problems when the bolt pushes them back.  The "9mm hammer" is not only somewhat notched, it's short front-to-back, so it can cause more problems.  A standard, rounded AR hammer works best in a semi-auto AR, and particularly in a 9mm AR.

With that said, there ARE aftermarket, "non-GI" style FCGs that appear to work well with 9mm ARs.  I haven't tried any yet, but I've heard good things about Geissele triggers in 9s.

I'm running the stock CMMG 9mm configuration. Really frustrating cause the CMC trigger is great.  Would the trigger in the CMC unit be stock AR? So the problem has to be in the 9mm bolt...maybe?

Sometimes it's how the geometries of the bolt and hammer interact that causes problems.  CMMG bolts are ramped, and they work great with rounded hammers. The CMC's flat, notched hammer may not contact the ramp on the bolt consistently, causing intermittent hammer resets.  

But it seems to me that it's almost certain that when the bolt goes back it's not always going back far enough to cock the hammer.  That could be the bolt and hammer, OR it could be something else.  What buffer are you running?  A lot of people just assume they'll need a very heavy buffer to run their 9mm, but my experience has been that Colt-style 9mm carbines (and my SBR) aren't that picky.  A standard carbine buffer runs just fine in my SBR...  So I'd suggest trying a lighter buffer before deciding that your hammer reset issue is because of the hammer itself.

I noticed that CMC says their triggers are "not recommended for use in the 5.45x39."  The hammer spring may not be strong enough for the 5.45's notoriously hard primers, which may also cause problems with some 9mm ammunition.  That's not your problem, but it's worth noting.

I put a JP trigger in my 9mm. Because it uses a regular GI hammer, it works fine. Price is a lot less than the CMC too, but more work to install.