There is a chance that the hammer is not hitting the nipple flat. That is why the #11 will not ignite on the first try. Check to see if the inside surface of the hammer is totally contacting the nipple when you release the hammer. With a musket cap there is more area for the hammer to hit, so it goes boom! On another note, # 11 caps for Goex, no problem, always good ignition. Musket caps for subs, although, I rarely use them.