This was posted on another forum

"However, I later found out from a post on rimfire central that there were two Canadianicon Privy Council orders for BSA Martini's for Cadets in 1925 (Order #440 for 1000 rifles, no model number specified) and 1927 (Order #2394 for 500 rifles, although these were specified as BSA #6).

The 1925 Privy Council order is believed to have been for Model 13 BSA Martinis which had the heavier receiver (similar to the model 12) but the shorter barrel (same length as the model 8); although there is no actual proof of this. Canadian BSA Martinis show C with an arrow stamped on the butt stock. BSA Martinis also have proof marks (as in the diagram below) with a capital letter ranging from A through V (only visible when the fore end furniture is removed)."

I hope this may point you in the right direction.