Worked with a guy that had a similar story...
His BB gun had jammed when he was a kid, and he couldn't get the muzzle to twist by hand. So he got a grip on it with his teeth, and when it did twist open, it went off in his mouth.
He said he made about 3 laps around the house before his Dad could catch him to see why he was screaming. His folks didn't see any damage from the BB, so they assumed he had either swallowed it or spit it out.
Anywho... he came back to work from the dentist appointment, told us the story, and said you could clearly see on the x-ray where the BB was still in the roof of his mouth.
One day I came home from grade school and was on our front porch and had the BB gun between my legs cocking it and evidently it was not fully cocked and I let go of the lever and it slammed it my family jewels. I remember vividly rolling around the porch in agony. My parents were not home from work yet and I don't think I ever mentioned it to them. Taught me not to cock the BB gun between my legs.
Also my younger brother still has a BB embedded in his thigh. Don't know if he ever told my parents or not. He did get me back at me later by embedding a dart into my leg. It's a wonder we all lived!