Problem is either the new upper carrier is not cocking the hammer back far enough to be caught by the disco,

To check this, charge the empty rifle B/C with trigger held back, shotgun the upper open while still holding the trigger back, and make sure that the disco is retaining the hammer.


Or, could be that the disco free gap to the hammer sear is not set correctly instead.

To check this, shotgun the upper open, do not touch the trigger, and cock the hammer back until it sear sear is as close to the disco sear at you can get it.

The free gap that the hammer sear edge passes by the trigger sear edge, should be .001~.003" (sheet of copier paper is .003").  If the gap is too wide, then either debris between the top of trigger and front bottom of disco that may be holding the disco open wider, or may have to re-time the disco to close the gap.


Also, make sure that that the disco spring was installed with large coil side down into the trigger slot (will need to use pliers to set it in place), and the hammer spring was installed correctly on the hammer and it legs are on top of the trigger pin.