Before you do any filing on the existing nipple, , first, first buy and install a new nipple. Now, put some lipstick, or inletting black on the top edge of the nipple. Lower the hammer down on the doped nipple, with the gun empty, and, obviously, no cap on the nipple. Pull the hammer back to full cock so you can get a good look inside the skirt at the face of the hammer. If the contact between the hammer and the nipple is right, you should see a RING of dye on the face of the hammer.
If you don't see a ring on the face of the hammer, but rather just an arc on one side, the problem you have with ignition is that the hammer is Not hitting the nipple flush. Instead, it bangs on the nipple, until the top edge is smashed lower than the other side of the nipple. This cause it to be hard to seat a new cap over the bulged side of the nipple, and it requires a first blow of the hammer to reform the cap to the shape of the nipple. Only then, will a second blow set off the ignition compound in the cap.
FIX: Go to a hardware store and buy a small slender grinding bit for " DREMEL" tools. You don't have to buy the dremel, altho' its a useful tool to have in any shop. The bit can be chucked in your electric hand drill. Grind away the dye area of the face, and keep remarking the face as you continue to grind away the dye. The dye is on the high side of the nipple. Eventually, a full circle will be achieved, insuring that you are striking the nipple squarely with that hammer face. AND NO MISFIRES! :applause: :grin: :hatsoff: