"If you are dry firing then the nock is breaking at release and any one of several things could be happening.
Nocks too tight, bad nocks (some older plastic gets brittle), previously damaged nocks."
The nocks are breaking at release, the nock pieces, are hitting me in the nose (drawn blood twice).
"Are the nocks glued on? Certain glues are not compatible with some nocks."
I have had glued nocks break, and treaded on nock break upon release. Most of the nock I have used are loose enough, they fall off the string.