You need to measure how far the trigger pulls back when the trigger group is out of the gun, and again when it is installed? If it goes all the way when installed, but the hammer doesn't move forward, it is most likely the safety is not completely disengaged. It works by trapping the hammer. Measure how far its actuator moves forward in the the trigger guard when the group is out of the gun and check that it is the same when the gun is assembled. If the trigger doesn't pull back all the way, then look for something that interferes with it. Watch that the little flat at the top back edge of the trigger doesn't run into anything?
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