Help wanted identifying a 20mm cartridge case


Book Reviewer
I seem to have inherited a spent 20mm cartridge case, allegedly brought home from France in '18 by my stepfather's father, who was a (non-flying) officer in the RFC from 1917. He was at home for WW2, as he was 53 when it started, so if this is a WW2 artefact it must have some other provenance. As far as I know - ARRSErs correct me please - the RFC never had anything heavier than the .303 Lewis gun in their aircraft and I have always assumed that 20mm only came in with Oerlikons at sea, and Hispano-Suiza aircraft cannon in fighters later in the WW2.

Base markings are as follows:

Rim of cartridge: 8, RL, DD1 3.468.B

Base of primer: 333, W8|28 with an M or W next to it, S and a theta in a square box, No 5 II N, a broad arrow in a square box, and a broad arrow on its own.

Here's hoping this means something to ARRSE ammo buffs.
You may have more luck moving this to the RLC or shooting thread.

Off the top of my head broad arrow could be the crows foot so Brit Mil.


Kit Reviewer
Book Reviewer
Pictures would really help as well.

They did try to put larger weapons on aircraft.. including the famous COW Gun...

COW 37 mm gun - Wikipedia, the free encyclopedia

What would be helpful would be the following dimensions...

Case neck diameter
Base diameter

Your markings would seem to indicate manufacture at the Royal Laboratories (RL) ie Woolwich Arsenal..

The first 20mm in UK air service was the Oerlikon in the 1920s which was found to be too heavy and switched to the Hispano Suiza...

You can spot the cases from these as the rim is narrower than the diameter of the case...


Book Reviewer
Thanks, chaps -


20mm case 001.jpg 20mm case 002.jpg

Length is 165mm, dia of base is 35mm. I have difficulty matching the shape of the case to any of the pix on the website Rampant quoted, largely because the base slightly (by maybe a touch less than 2mm) extends beyond what will be chambered; and also the shape of the 'shoulder'.
Maybe post your photos on the Great War forum under the "arms" section: thats one of the forums where TonyE posts, who is a leading authority on munitions.

Great War Forum

Actually, TonyE is around here somewhere as well... show an ammo case or an interesting bullet, and he'll pop up like an ammo genie....
Looks like a WW2 blank of some sort, but beyond that I am beat. The codes are not in my books. Not heard of many blank 20mm either, wait for Dingers opinion is my best suggestion
HE117 is probably better with this, he did Initial Acceptence on stuff like this.

The reason for two sets of markings is there are two components - the primer and the empty cart case details.

On the cartridge case:

.8 is the calibre (in inches)
RL is Royal Laboratory
DD1 3.468.B - not sure, it could be a date code or it could be filled lot details amongst other things.


Looks like No5 Mk2 (model number).
Things in Squares are often proofing marks (IIRC).
333 is probably the lot number
W8/28 could be the type of propellent, but could also be part of the lot number.

Can't find a reference to a weapon that used a Cartridge Case with those dimensions.

Best guess would be an Engine Starter Cartridge.

Will keep digging.
Very strange...

1. Definitely British

2. Not a standard 20mm cannon round (no rebated rim) - a rimmed/flanged case is rare in these calibres, and would indicate a design date of 1890/1900

3. Separate primer which indicates a high pressure round.

I'm not aware of necked starter carts unless they are modified conventional cases... (why would you?)
I'm thinking Anti-Tank rifle.

This isn't necessarily WW1.


I'm thinking Anti-Tank rifle.

This isn't necessarily WW1.
In that case then (pardon the pun) I'm thinking **** firing or carrying it!
I'm thinking Anti-Tank rifle.

This isn't necessarily WW1.
With an RL mark, I don't think it will be much later - Woolwich basically shut down ammo production after WW1 when production was dispersed to the ROFs. The only Brit AT rifle produced between the wars was the .55 Boys Stanchion rifle, which has a belted case...

Not sure we had much call for Anti Tank before WW1 :)

To be honest I am thinking possibly naval sub cal or spotting rifle.. the N on the primer could be Naval service - I need to trace the No 5 primer in the L of C and see what it was approved for!


Didnt Woolwich retain the experimental pre production ammo jobs in the same way that Enfield was kept open by repair work between the wars?
I thought it might be a point to work from, but then couldn't develop it.

It's bloody "Ex What's It" all over again. I got the bloody torpedo last time - just sodding great when your whole course is geared around Land Service Ammunition.

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