I could really go for a sealed box and a handful of loose rounds...... it's wartime and it's a headstamp I don't have.
Interesting: in the old days, the Brits used to make blanks out of just about anything at all that they had left-over and lying around. I have found several very rare headstamps in old lots of blank ammo, and that includes a CANADIAN headstamp for the Cordite Mark III, which was a soft-point in the Dum-dum series and generally not known to have been made in Canada.
Dedicated production of blank ammo all should have a headstamp that shows the code letter "L", which indicates Blank ammunition.
No code: Ball, but there will be a Mark (VI, VII, VIII or 7 or 8)
Powder code: C for Cordite, Z for Nobel neonite or some other NC powder
Blank: L
Tracer: G, generally with a number; there were navu and army, day and night tracers
Armour-Piercing: P for the really early stuff, middle of War One, supplanted by W late in the Great War and most often seen in the standard W II version, which continued to the end of production
Incendiary: code letter B, comes from Buckingham, which originallh was made for torching Zells. A really interesting variant is the B IV and B IV Z, which is an armour-piercing tracer incendiary designed for torching the self-sealing and armoured gas tanks on ME-109s. This stuff is very rare, although the Government gave away buckets of it during the War for target practice, ebing that only really fresh stuff went to the Hurris and Spits. It is likelt to be even scarcer, now that free Canadians are not allowed to own it. I have actually seen a couple....
Blanks are sort of like politicians.... a lot of noise but you don't dare take them too seriously. Still, they can be interesting.