I had a cheap little blackpowder pistol manufactured by the company who made the cobray 9mm assault pistols. Got it to play around with. I use to have to use two hits on the #11 nipple to get the cap to go off. Either the nipple was too big they provide or the caps too small(brand). You say the cap crushes then fires. If so, it sounds like it isnt seated all the way down on the nipple and the first hit is just seating the caps ignition compound closer to the nipples top. I couldnt see the nipple crushing unless it wasnt supported. Has to be worn nipple, nipple size, or cap size. Some #11 brands are actually tighter than others.