Mr Laidler a question.

Did this occur with hard used No.4 rifles also, or was this a No.5 issue only?

From your article titled: No.5 Wandering Zero?

"You could always tell the high mileage rifles, apart from the
shot-out barrels because the backsight axis pin retaining pin (longest
name of a part on the rifle. The PIN, retaining, pin axis backsight) was
always sheared where the bodies had expanded at the rear and sheared
it. So, if at the moment of firing/and max pressure/load the body
spreads at the rear, especially during a gun battle, I suppose it would
upset the balance between the locking lugs, bolt and cartridge seating
on the bolt face."

Thank You.

Never saw a No4 pin retaining pin axis backsight shear through continual shooting. Only on No5's. Mind you, seen a few sheared because amateurs just try to drive the backsight axis pin out without removing the retaining pin. But that's another matter!