check the nipple on the rifle. Sometimes the top will flare and it makes seating the cap hard. Often you will hear people about saying the first strike of the hammer sets the cap. The second fires it.

Try a new nipple if that is the case. Another thing is what cap are you shooting? If they are CCI standard, that might be your problem. Also make sure they are #11 and not #10.

Also when it does "splinter" the cap is it firing that cap? But the fun fails to fire? Or is it just hitting it and setting it? Pick the nipple with a nipple pick. Then cap it.

Last, what kind of powder are you shooting?