That was fascinating but incomplete. The actual strength of the Lee Enfield, especially the No. 4, has not been questioned too much but the rigidity has. There were no measurements of the fired case to gauge the amount of stretch which would have been interesting. However, because of the fractured lug, any findings would be invalid anyway.
The Lee enfield action flexes. This is demonstrable. The thing is this; the flex is why it works so well for the intended purpose. If a cartridge is a little on the tight side, the bolt can be closed on it because the action flexes and because the locking lug seats are angled which provides a lot of force. The lugs on the P-14 are angled as well but the P14 does not flex so the same scenario may result in a jam.
In this case the fractured lug probably occurred during the second 7.62 proof firing but did not show up until it failed. Close inspection when the gauge first indicated an increase in headspace might have shown the crack. Forcing the bolt down on the gauge may have hastened the failure.
I have fired a No1 MkIII to failure and the lugs never did fail. The bolt actually bent and the bolt head was partially sheared away by escaping gas. I don't recall what the final load was but it was well beyond what one would expect any rifle to handle.
A neat video but I will second the request for the buxom blonde. GD