Put some marking black, or lipstick on the top edge of the nipple and lower the hammer down onto it, to mark the face of the hammer where it touches. Then cock the hammer back and see if you are looking at a complete donut, or just an arc. If its the latter, you need to use a dremel tool with a grining bit to remove the high spot- shown by where the marking black, or lipstick is left on the hammer face- until you get a complete donut hole. Then, you do have to remember to use a cleaning patch after each shot to wipe off the nipple before putting the next cap on. If you allow crud and carbon to build up, you will get a nipple that will not allow you to seat a cap all the way down on the nipple, and the next hammer fall will simply seat the cap, but not fire it.
paul