I suspect the cap was already loose, but it does cause quite a bit of shock. LOL, great story for the dentist though. I shoot my S&W 629 V-Comp at the indoor range and it usually draws a crowd. It also sends everyone in the nearby lanes scurrying for a lane change which is why when I bring my .50 Beowulf I request a lane with nobody on either side for a couple lanes lol, fortunately haven't popped and caps or crowns lol. I started doing that when one poor lady who was in the next lane developed a flinch that she probably still has today. She was there with her husband who was actually doing the shooting and I warned them before shooting it was going to be really loud and would rattle the walls, they both said no problem it wouldn't bother them.
I started shooting and after about 4 shots my sister tapped me on the shoulder and I looked behind where there was a whole crowd of people crowding the window to see the crazy lady shooting her hand cannon and AR cannon, including the same poor woman who was smiling but twitching like a Tourette's victim coming off meth and I felt terrible. So after that I started requesting lanes away from others when shooting big bores and .44 magnums.