Hi all,
Having looked at Peter Labbett's book on British military ammunition, and spoken to a fellow collector of British ammo, who has been collecting and researching for far longer than me, I believe that this Cordite load for the carbine is strictly commercial. The military ones were admittedly only made by the Trade (mostly Birmingham Metals & Munitions, and Kynoch), but had either military-style headstamps (e.g., K C I) or were unheadstamped.
The commercial ones are not too uncommon, and can sometimes be found in their red & yellow commercial packets, but I have not managed to find a proper military one in 30 years of collecting!
Regards,
Roger.