J.I.W.
Thanks for the upgraded pic of the fired case. I have roughly orientated that headstamp to a layout one would normally see - and I have done similarly with a .303" Mk.II Cordite ball. We can see that the "C" (Cordite) on your sample is slightly crooked:
A bit of a puzzle as to why the bunter maker would have done so.
Regarding the manufacturer's code being identified by Bester and Rob D as BM@MCo, That is indeed suggested by Edwards in his Ammunition Manual No.2; which is probably where Bester got his ID from. However, Peter Labbett defintely identifies manufacturer's codes consisting of a single Arabic numeral (1 to 6) on pre 1904 .303" as being cases supplied on contract to Woolwich Arsenal and filled there.
It must be remembered that upon the ontbreak of the ABW, the army was very short of suitable ammunition and had to resort to"The highways and byways" to supply the minimum of three million rounds per week (as in Pakenham).
Regards
IL.