Ditto, chances are you are bump firing the weapon.



To really understand why, shotgun the upper open, hold the trigger back, then over cock the hammer to the disco, slowly release the trigger and see the distance before the trigger comes all they way back forward that the hammer is released from the disco and caught by the hammer.

Hence ideally, you want the hammer to be released from the disco on trigger release just about the point that the trigger is all they way back forward at it rest point, and with some FCG's, the disco releases the hammer way before this point, making it very easy to bump fire the rifle by accident instead.

Also to point out, the FCG is not to be used with 9mm rigs; but not sure if this is due to the hammer shape itself not working with the rigs, or the fact that the 9mm bolt will slam home harder, and the FCG may release the hammer on the harder jarring impact instead.

Yep, and the reason that CMP two stage triggers have the long take up on the first stage,  since it this allows a long over travel forward of the trigger before the disco will release the hammer on reset, then the distance that is needed to pull the trigger back after reset (first stage) before the trigger will release the hammer at the second stage wall instead.  

So what is going on in our case, you dancing your finger on the trigger enough during cycling to fire the rig again as the bolt locks up, hence bump firing the rig.  
To prove this, fire the rig while holding the trigger back tight during ignition/cycle, and make sure to not release the tension on the trigger all the way back until the bolt has fully locked closed.  This will weed out if the problems is you bump firing the rig via the trigger dancing with your finger, or if the disco is just not retaining the hammer correctly during the cycle, and the B/C impact jolt enough to dance the hammer off the disco with the trigger retained all the way back to fire the next round instead.

Also, make sure that you have the trigger installed correctly, hence the set screws. then jam screws set so the trigger pack is not dancing on the through pins/in the lower receiver cavity void and causing some of the problems.  Also, with the pack installed correctly and trigger pulled all the way back, make sure that the trigger is not limiting out on the back slot of the lower receiver slot for the trigger itself.

Again, from the web site, will not work in 9mm.  Again, could be that the hammer does not have the needed clearance, or due to the impact increase of the blow back action to the barrel on closing.

As for the one that has me questioning the lower receiver, with the set screw tight against the bottom of the receiver to draw the pack tight on the receiver pins, this should not cause problems with the selector.  Hence the problem could be that the selector is milled to low in the receiver, and with the pack tight against the pins with the set screws all the way down to hold the pack tight against the receiver pins, this is reducing the amount of over travel on the trigger with the selector on fire, which is reducing the amount that the disco will engage the trigger with the hammer all the way back isntead.

Bluntly, with the set screws tight to pull the pack tight against the receiver pins, and the hammer cocked back, you should be able to flick the selector safe to fire and back, but with the selector set to safe, when you pull the trigger, the hammer should not release from the trigger sear. If this is not the case, and you can not set the selector to safe from the fire position with the hammer back, then get the supplier on the phone to see what corrections need to be made. Also, while you have them on the phone, verify the 9mm problem and if it an inpact issue, or that the pack hammer does not have the needed clearance instead.

Colt 9mm hammer for semi auto blow back action rigs that go hand and hand with the blow back semi auto bolts shown on the bottom,