My first thought is that you have an out of spec hammer that is sitting up too high at full cock. If it was holding in the right place, a cutaway carrier should not matter, nor catch the pin.
If it is only doing this when your holding the trigger back, the disconnecter, which would be holding the hammer back at that point, may be worn. On the other hand, if it does this when you're just operating the action to load the chamber (or whatever)the top of the hammer is sitting too high.
You can probably do a quick fix by using an M16, rather than AR, firing pin. The smaller collar on the M16 pin probably won't catch the notch on top of the hammer. My own recommendation tho would be to replace the hammer. The new DPMS hammers do not have the notch in front, so there'd be nothing to catch on.