On new .303 British Lee Enfields an oiled proof pressure cartridge was used to seat the lugs and bolt head. After setting the headspace as close as possible to .064 the rifle was proof tested, the Enfield was then checked with a .067 head space gauge and if the bolt closed on this gauge the rifle failed proofing due to excessive lug setback.
An oiled proof cartridge seated the lugs to the receiver and this is why your chamber should be kept oil and grease free because oil doubles the bolt thrust and can damage your rifle.
Also on the No.4 Enfield the replaceable bolt heads only went to a number 3, the reason for this was simple, it was found that by the time a number 4 bolt head was needed the receiver lug recesses had worn through the case hardening and the rifle was sent for overhaul.
Did you ever wonder why Savage-Stevens rifles have a bolt head the pivots on the bolt?
(when the bolt is closed "both lugs bear evenly)
Eat your heart out..................and why lap your lugs when you can stone the bolt lug to fit???