What numbers and / or letters are on the bolt-head?

Asking because, in the early 1950's, Lithgow made a short run of "over-length" bolt-heads; a concept similar to normal practice on the No4 series.

Before that, there was ONE, (count them) ONE "standard" bolt-head with known tolerances The ONLY notable difference was that the early ones were made from "malleable cast iron" and later ones, particularly in Australiaicon, were made from "mild steel", suitably case hardened and identifiable as such by a sans-serif, upper case "M". These went with ONE receiver Body and ONE bolt body and ONE barrel, all of which had to be hand selected and fitted / matched via some very expensive gauges, to build a mechanism that was to overall dimensions and tolerances. VERY Nineteenth Century.

Oz was using the No1 Mk 111 Sniper rigs until the mid 1970s. Oz Infantry units sent off to the Great South-East Asian War-Games took their SMLE sniper rigs. However finding MkVll ball ammo in country was a bit of a challenge. And the Patt 18 (Aust) optics were not quite at home in the local environment and optically WAY behind the Weaver and Redfield / Leatherwood units starting to appear in theatre. The information on those "extra" bolt-heads is to be found in the workshop instructions also still being issued in the mid 1970's. I vaguely remember posting that workshop instruction and bolt-head table somewhere here, a few years ago. I'll go for a little "dive".

Cheers.