Thanks Pedro, - did you notice that the "Mark One" symbol underneath "RL" was the early patten of a horizontal "I", which compares with later vertical "Mark One" symbol next to the "P"?
I thought that the "A" in a circle might mean that it had been annealed, but I'd previously only ever seen the annealing stamp on the base of brass shell cases. It might be sensible if the plug was ever re-used - it certainly looks like it's had some other later stamps which could signify some changes or repairs. Another observation was the apparent "coppering" of the plug which didn't show any sign of brass underneath when I cleaned it - perhaps made of bronze, but again I've never read of that.
A final additional observation is the two holes, possibly filled with lead - if so, why? I wouldn't have thought that the weight of the plug was particularly critical - unless someone knows if it was?
Depotman
"Note.—All Plugs, base, shell, are stamped on the base with their
number and numeral, and the letter “ P .”
Plug, base, shell, Nos, 1, 2 and 5, supplied by the trade are examined
and weighed.
Those found correct to weight are stamped with “ W.”
Those of incorrect weight will be stamped with C .”
Those marked “ W ” are suitable for storage or for firing in filled
shell, whether filled with powder or salt.
Those marked “ C ” are suitable for storage, but must be used in
salt-filled shell only."*
Yours was marked C indicating it was sub weight. The lead was added to correct this which is why C is crossed out and replaced by P. Plugs are made of gunmetal (bronze derivative).
Circled A means annealed, with respect to Cart Cases, so I see no reason to not apply this symbol to your plug. Annealing maybe was done before the drilling and re-weighting with lead.
Weighting would be criticial where plugs are used for firing practice projectiles.
* Treatise on Ammo 1915
