Is your nipple completly clear??? (can see clean hole through it)...I like CCI mag #11s....and I drop the hammer down lightly push the cap on for a good seat....never never had problem with them going off. TC makes a SS nipple that has a slighlty larger firs hole....could try that too
There is another manufacture of #11 caps that are real hot too...cant remember the name....its German and the tin cover is red.