I came about 1/2" from possibly loosing my right eye to this mistake. I was still a newbie, and I thought that a nipple was a nipple. I put a foreign nipple (CVA or Traditions, I can't remember) in my White Mtn Carbine. Worked fine for about 10 shots. When it let go it had enough force to cock the hammer and the nipple hit my right eyebrow with enough force to draw blood. I found the nipple and the threads, which are too small and don't grip well enough, were sheered off.

That was a hard lesson learned.

Mike