20 MM Question

Hi, just picked up a 20 mm x 110 round. The projectile is completely painted red. The unscrewable fuze is unmarked. Head stamp says MP 1944, with the letters A.L., then an anchor. On the bottom is 20 - MM - Mk - 4. I dont know if its a Hispano or an Oerlikon and was used in aircraft or aboard ship.

I looked on Tony Williem’s site and read about a 20 x 110RB USN. To me, my round appears to have a rebated rim. I measured my rim dia and it was 29. The one that Tony listed as 20x110RB is 24.

The fella i got it from has an almost idenitle round but that rim is almost the size of the head. He did say that round was used by the US Army. Thanks in Advance


A red projectile indicates HEI - Tetryl.

Sounds like an Oerlikon Mk 4. But, I’m confused about the measurements of 29 and 24. 29 what?? 24 what??


I assume they’re the rim diameter in millimetres…

  • Ole

Hi Ray, Thanks for You Reply. What i was talking about was the MM of the RB rim. I just meassured it again and i came up with 21.95 MM. Mybe my caliper is starting to act up. It does look like its electric primed. Maybe for aircraft use?

22 mm for the rim diameter is more like it.

Are you sure it’s electric primed? The primer had a heavy ring crimp that could be confused for something else.

Aircraft were not typically armed with 20mm until after WW2. The date (1944) on yours seems to preclude aircraft use. They (aircraft) were electric fired but the gun was completely different than the Oerlikon.

I’ll admit that I’m not very comfortable with my ID. Maybe someone else can help.


Hi Ray,

Thanks Again For Your Replys.   The primer does have a a heavy ring crimp.   I am the one that doesnt know what i'm talking about.

Over the years i've learned a lot from your posts.  Thanks Again and Take Care,   joe

The April 2010 “Cartridge of the Month” shows all three of the 20 x 100mm cartridge types.

Let us know which one you have.

From the headstamp: MP = Metallic Products Corp., Closter, N.J. They are listed as having manufactured Oerlikon Mk 2 brass cartridge cases from 1942 to 1944.

Joeinco1 can you confirm the headstamp on your case is “Mk 4” and not “Mk 2”?


Thanks for the link on 20 x 110 JohnS. I have not found the exact round. The round that i have has the entire projectile painted red.

Thank You Too bdgreen for trying to help me sort this round out. The headstamp on the round i have says MK 4. i also wonder what A. L. means.

The fella a bought it from has another 20 x 110 but the rim is bigger and is not rebated. He mention the round differed from the Navy version and was used by the US Army.

Many Thanks

I work a couple of miles from Closter,NJ, I can walk there and ask :)

10-4 & Thanks, But Please Dont Go Out Of You Way!

I have 2 of the Mk4 cartridges. One headstamped TACU (The Aluminum Cooking Utensil Co.), and the other NOEN (no idea). There’s no doubt in my military mind that they are both legitimate. I think Joe’s is also OK .


Thanks Ray. But what about the other 20 x 110 with the bigger rim? Did our US Army use them? joe

NOEN = Naval Ordnance Engineering Laboratory.

[quote]From the headstamp: MP = Metallic Products Corp., Closter, N.J. They are listed as having manufactured Oerlikon Mk 2 brass cartridge cases from 1942 to 1944.

Joeinco1 can you confirm the headstamp on your case is “Mk 4” and not “Mk 2”?


Brian, that identification comes from a wonderful list published long ago, but it had a few mistakes and ommisions, and this one is one of them. The correct manufacturer is Motor Products Corp. in Detroit, Michigan, which was the same company that made nose and tail turrets for the B-24 Liberator.




The USN used Oerlikons. The other cartridge is a Hispano and I can’t say who used them.

One thing that still confuses me about your cartridge is the paint. Red indicates HEI but it was the designated color for the Mk 3. Mk 4 were usually painted gray or blue for HET. Does the paint on yours look original? Sometimes a collector will paint a projectile with whatever color looks the prettiest. Unfired projectiles were usually dummies or otherwise never loaded, originally. The military was not in the habit of removing a fuze, deactivating it, and dumping out the Tetryl or Pentolite.


Thanks for checking the headstamp.

Thanks for the update on the identification of manufacturer MP.

This doesn’t surprise me, in reference to the manufacturer NOEN identification given in the above post as “Navy Ordnance Engineering Laboratory”, 2 older manufacturing listings I have indicate NOEN to be Northern Engraving & Manufacturing Co. LA Crosse, WI. (producing the Mk2 cartridge case from 1942 to 1943 and the Mk 4 cartridge case from 1944 to 1945).
And from the thread: viewtopic.php?f=8&t=10339; Darling2 posted the following: “I have a paperweight, or what I believe is a paperweight, it is a wood block with a 20mm Oerlikon casing bolted to it, headstamp is NOEN 20 M.M. MK. 4 1945. There is an engraved plaque on the front that reads 100,000,000th Oerlikon Cartridge Case Made By Northern Engraving & Mfg. Co.

But others indicate NOEN = Navy Ordnance Engineering Laboratory, Dahlgren, Md. For example see: bocn.co.uk/vbforum/threads/9 … ot-of-20mm.

So which is correct or did both produce 20mm Oerlikon cases during WW2?


PS- Doing a search on GOOGLE gives no results for “Navy Ordnance Engineering Laboratory, Dahlgren, Md”. The closes result is the Naval Ordnance Laboratory.

From the dreaded Wikipedia:

“In 1929 the Mine Laboratory was merged with the Experimental Ammunition Station in Indian Head to form the Naval Ordnance Laboratory.
NOL began slowly, and it was not until the beginnings of World War II, when Germany’s aircraft-laid magnetic mine began to cause serious problems for the Allies. As the importance of NOL’s work became apparent, it also became apparent that there wasn’t enough space at the Navy Yard to accommodate the necessary research facilities.
In 1944, acquisition, planning and construction work began at a 712-acre (2.88 km2) wooded site located at 10903 New Hampshire Avenue, Silver Spring, Maryland. Someone remarked to a Navy official during early 1945 that it seemed odd to be building the new laboratory at that time: the war would probably be over before the facility could be finished.”

Sounds more like a research facility than a production facility and so late in the war.


I think that the US used the Hispano exclusively as an aircraft gun during WW2. Both USN and USAAF planes used it, the main USAAF aircraft being the P-38 Lightning (one 20mm Hispano plus four .50 cal) and the P-61 Black Widow night fighter (four Hispanos). The main WW2 USN plane carrying these guns was the SB2C Helldiver. After WW2 the USN made much more use of it in arming planes, the USAAF/USAF not so much.

The last I heard the Hispano was still in use as a light deck gun with the US Coast Guard under the designation MK16. See: navweaps.com/Weapons/WNUS_20mm_mk16.htm

The British RAF did of course make far more use of the Hispano during WW2 and for a few years thereafter. The US had a lot more trouble with it: see quarryhs.co.uk/US404.htm

Just for reference - from a British 1943 manual:

Brian, NOEN definetly stands for Northern Engraving & Mfg. Co. Below you can see a picture of the Oerlikon plaque: