Just had a long conversation to the former Chief Examiner and technical writer regarding the No7 bayonets of the era about whether the bullet could ever in reality, strike the crosspiece. It couldn't unless it was a 'set-up' trial. BUT he did concede that it was always suspected that the muzzle blast from a No4 rifle fitted with a No7 bayonet would definately strike the crosspiece which definately COULD and WOULD loosen the crosspiece which was fixed to blade which was in turn, rivetted to the grip tube. And once the rivets were re-tightened it became an unfixable lost cause!
This blast effect would not affect the integrity of the bayonet when used on a Sten gun. From this you can understand that while the bayonet looked good on the No4, to shoot the rifle with it fixed was the death knell for the bayonet.
Interesting if you think about it.
Added later: Parts list picture of bayonet stripped shown in back part of Sten Gun book