Unknown, potentially 42mm brass case, British?

[Vasco Da Gama]

This interesting case turned up recently and I have no idea of an identification!
I think it is unfinished, the primer pocket remains to be created and there are no markings. I acquired it in the UK, so potentially British and a research project? I would offer the work and material involved suggest it is not home made, over to you!
Mouth diameter 42mm, length 285mm, rim diameter 52.9mm and rim thickness 5.1mm.
Pictured next to 37mm Flak round for comparison.

 

[tigbrand]

Looks similar to the red king exp case with that base and large extractor groove. try searching red queen.

 

[Tony Williams]

It's one of these (from my new Autocannon book):

2-POUNDER 75 CAL (40 × 277RB)


In February 1943 work began on a Bofors replacement for the Royal Navy, intended to deliver a higher performance in terms of both muzzle velocity and rate of fire. B.S.A. was given the job of developing the gun, which was designed around an unusual cartridge from the British Design Department. The case was wide for its length and with a sharply rebated rim, suggesting that the gun may have been an API blowback (in other words a scaled-up 20mm Oerlikon). The round was officially designated (and headstamped) the ‘2-pounder 75CAL’ and was made at the Royal Laboratory, with 1944-dated cases existing. The project was abandoned in 1946 and while 1,000 cases were ordered it is not clear whether or not a gun was made, or only test barrels.


The round is approximately 425mm long and weighs around 2.3kg without propellant; data varied somewhat as development proceeded. The projectile weighed 900g including 100g RDX and was designed to be fired at 914m/s.

 

[Vasco Da Gama]

Many thanks Tony, excellent information as always.
The case is very heavy, I understand there is additional material in the base which would be removed for the primer. I will weigh it and compare with a standard 40mm L60 Bofors case. Happy to be corrected, but a heavy case would help in a gun operating on the API principle?

 

[Tony Williams]

The case is very heavy, I understand there is additional material in the base which would be removed for the primer. I will weigh it and compare with a standard 40mm L60 Bofors case. Happy to be corrected, but a heavy case would help in a gun operating on the API principle?

It could do, if the weight is in the right place. I have seen a sectioned example of the case, and the weight is caused by a very thick base. The strength of the base means that it will be able to withstand the chamber pressure without being fully supported by the chamber, which could be a useful characteristic especially with a high rate of fire.

 

[Vasco Da Gama]

Thanks Tony, as you say the weight appears to be in the base of the case, my estimate is the 2pdr 75cal case weighs about 1.3kg against a 40mm Bofors case of about 0.6kg. That is a lot of additional brass for a fast firing weapon and cannot have been sensible in wartime unless the performance gain was significant. Couple of extra photos for interest.

When is your book Autocannon due for publication? Don’t tell me I have missed the boat!

 

[Tony Williams]

Autocannon should be out next month. It's already been put back a few times, though, so don't hold your breath.