I'm sure it was a Lee Enfield and not a P14 as part of the bolt was mentioned to have struck the son and in a P14 the bolt head is fully supported inside the receiver, and the bolt handle provides a 3rd safety lug that locks into the rear of the receiver. P14 are super strong actions and I have never heard of a bolt failing on them but they will rupture the receiver when a catastrophic failure happens with a overload.
It is common for the Lee Enfield rifles to suffer bolt head damage and bolt head failure with break up and then shrapnel of the bolt head, extractor and spring and screw when something goes wrong as it is a 2 piece unsupported weak point in the bolt lockup of these rifles, more so than most turn bolt action rifles.
I also think the original writer is wrong for thinking or calling it a "out of battery" firing, as Lee Enfields will not fire until the bolt is closed and handle is down.
Maybe these pictures will help show what happens with LE bolts when they fail -


It is common for the Lee Enfield rifles to suffer bolt head damage and bolt head failure with break up and then shrapnel of the bolt head, extractor and spring and screw when something goes wrong as it is a 2 piece unsupported weak point in the bolt lockup of these rifles, more so than most turn bolt action rifles.
I also think the original writer is wrong for thinking or calling it a "out of battery" firing, as Lee Enfields will not fire until the bolt is closed and handle is down.
Maybe these pictures will help show what happens with LE bolts when they fail -























































