"SM126 Armourer's plug gauge .308" - Barrel leed wear at commencement of rifling. Vickers gun - inserted at chamber end. Must not enter more than 0.25 inch. This is indicated when the screwed end of the gauge is 0.30" proud of the breech. Rifle No. 4 - Bore reject - Not Go - (1) Shall not enter the bore at the muzzle end more than 0.25 inch. (2) Shall not completely enter the chamber end at the breech."
"Plug Gauge, NOT GO 0.308in. .........(1)Shall not enter the bore at the muzzle end more than 6.35 mm (1/4 in.); and
(2) Shall not completely enter the chamber at the breech end."
(National Defence Canada, "DATA SUMMARY RIFLE, .303 CALIBRE, LEE ENFIELD, No 4, ALL MARKS" page 8)
Rifle No4 All marks and Rifle No5
Armourers Plug 0.308" (Reject diameter of bore applied at the Breech)