Sounds like the trigger yoke is dragging on one or more of your mags. Do some of them not fall cleanly from the gun? Use smoke or Magic Marker to note if there is contact. Also check that the grip safety is actually disengaging when it is depressed. If you have a spare, cut off the leg of it that blocks the trigger's rearward movemnt. Also, look very carefully for debris that could hang up movement, and stake the hammer strut pin in place. It can move sideways and cause problems. Beware surplus parts, particicularly disconnectors ans sear springs, and make certain that the sear spring is positioned properly, its lower curve in the slot in the frame, the upper legs engaging the sear and the disconnector. If your gun has the firing pin safety, make sure that no debris, burrs or deformation in the area of the plunger is preventing free movement of the parts.