"I am the person this happened to. The 7th round jammed, which is nothing unusual for this gun. It happens all the time. That is why I didn't really hesitate to shoot the final round. We were using newer ammo, so we don't think that's the problem. My brother has been looking at his M1icon, and we noticed it will still fire with the chamber not fully closed. The chamber can be open up to 1/2" and the weapon will still fire. We think that's what happend."

This is the quote from "arizonagirl24" the unfortunate shooter on You Tube. I think this is what she is referring too - I have pulled the trigger on a Garand with a slightly opened bolt with a primed (BUT NOT LOADED) cartridge case several times. The firing pin drops loudly, and the bolt is noticeably shoved forward, giving the impression it would fire. But the firing pin does not detonate the primer. There is only the very slightest indent on the primer. So the receiver bridge and firing pin / rear bolt design prevent the firing pin from detonating the primer. (Someone more familiar with the design can describe the safety feature better.)

I tried to join You Tube to ask more questions and encourage them to get it checked out by a qualified expert, but Google owns You Tube and wants your birth date in order to register. Sorry but I am unwilling to give that to an internet based company. So to me either the gun was seriously (and rarely) out of specification, or the ammo was bad. Based on her statement and the video I do not believe it was a squib on the 7th round that caused this.