Those drawings form part of the documentation issued to armourers, in Australiaicon, at least, during the 1930s.

I have one of those "Boxed Sets" on my shelf. It came from a bloke whose dad was the original WW2 Armourer Sergeant recipient, and his details are noted inside the lid of the box. This set is noted as having, "Three additional plates added from amendment No. 2 to Supplement No. 2 (1942)"

Others in the set include Lewis, Hotchkiss, SMLE, (of course), Bren, Webley revolver, BOYS Mk.1 etc. There is even a little chart of instruction for fitting the Auxiliary spring to "Magazine, Bren .303in M.G. Mk.1" and also a guide to setting the lips on the same mag.

The P-14 chart has some interesting details:

"The (F) rifle is fitted with fine adjustment backsight.

"The [T] rifle has the fittings for the Telescopic Sight, Model 1918, otherwise it is identical with the [F] rifle except that in the [T] rifle the aperture sight stem and sight dial pointer are removed."

The charts essentially provided parts identification to armourers.