Originally Posted by
enscien
The Enfield 7.62mm barrels and later .303" barrels had the shoulders cut back to accommodate a thick breeching washer used to control breeching up by the 'constant torque' method. There is a very good account of this on page 185 of 'The Lee Enfield Rifle' by E.G.B. Reynolds (long out of print).
As I recall, (from watching the operators doing it) the breeching washers came in thicknesses of about 0.060" to 0.080" in steps of 0.001". A thickness of 0.074" would be typical. At RSAF Enfield they selected the thickness which would allow you to screw the barrel onto the body hand tight, leaving a further 18.5 degrees 'breeching-up angle' for tightening to the vertical position with the breeching up wrench. The torque required to do this should then be 120 +/-5 lb-ft.
This was a post-war development because it was thought that slightly bulged chambers were resulting from some barrels being over stressed by having to be screwed in with an excessive amount of torque because the breeching up angle was too high.