I have a 19-5 that I picked up the other day that misfired constantly. I changed the mainspring and strain screw (both were not factory original) and the misfires improved somewhat. It still misses a couple of times per cylinder. I measured the cylinder-frame gap with an empty case in place and it was the same as my 66-1, as was the barrel cylinder gap. It has minimal end shake and locks up pretty tight. The hammer hose OAL is slightly more than 66-1 and 15-4. Does anyone have any other ideas as to what would be causing the missfires?