he's lucky there wasn't more damage to the weapon AND himself. I have not used the ammo you mention but I hate any type of light loads. I'm glad the boys are OK. I'll bet both will be a little more attentive to loads that don't feel quite right from now on. It only takes seeing something like that once to really get your attention. I was shooting with a guy that was using some of his hand loads and for some reason was loading light. He had a squib and was about to fire again when several of us about dove on him. I've been around for a couple KB situations and hope to never see one again. Whenever I hear about one it makes me take pause.
Again. I'm am happy to hear the guys were not hurt. Shooting is a great sport/activity. But we have to be careful and always pay attention. I hope that thew new shooter was not put off by the experience.