The other was a 6 shot semi-automatic 12 guage. on the 3rd or 4th round (attempting to rapidly fire all 6) the cap on the end of the ammo tube (or whatever it is actually called) came off and the whole thing just went to pieces.
Luckily I was not injured in anyway from either instance.
Pretty sure, its a magazine cap. The one on my Remington 1100 comes loose when I am shooting trap. I tighten it after about 4 or 5 shots.
Therein was your problem. The cartoons at the end of the barrel obstructed the flight of the bullet...... 8~)