AMT Backup .380...... Three trips to the gunsmith and twice to the factory could not make this thing go BOOM.....click click click....BOOM....click...BOOM....click click. (you get the idea)
LOL! I ran into that problem in the 80s when I was still working. Our shop ordered 6 from AMT, out of which exactly one would fire.
I went crazy looking for a solution (stronger hammer spring, lighter firing pin return spring, slight enlargement of the clearance slot on the fp, etc., etc.), but finally had an epiphany one day.
The problem was that the hammers had been cast slightly oversize, and, when the trigger was pullled, the front of the hammer was dragging against the sear, slowing it down enough so that the pistols wouldn't fire. Some slight dressing of the oversized front portion of the hammer and, voila!, they all fired reliably after that.