First off welcome to the forum. It is good to have you here.

Breaking nipple by splitting in half.. WOW!! In all my years of shooting, I have never had that happen. Does the hammer spring feel really strong? Were these old nipples? If the hammer off center? Did the hammer try to reset itself when it did fire? Were the caps going off properly? Were you having misfires?

First thing I would do is get a Stainless Steel Hot shot nipple and try that again. If it happens again, then contact Traditions and tell them about it.