Info on 20mm casing?

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ny32182

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I have an online acquaintance who has a 20mm casing that he describes in the following manner:

So I have a 20mm shell my grandfather brought back from WWII. He flew B-24s, and we always figured it was from one of them, but now I'm pretty sure there were no 20mm cannons on the B24.

It's about 4.25 inches long (108 mm) and on the flat part of the bottom, it says "20mm 11K - .2 1943" Then it's got a tiny B with a circle around it.
Click to expand...

Here are a couple pics:

IMG_0704.jpg

IMG_0735.jpg

So, what can we tell him about it?
 
After a little research here's what I've found.

I worked on the M61A1 20mm system for f-16's in the Air Force and can immediately tell you that the casing you have is NOT the same. The case neck does not have a sharp enough shoulder.

I found this photo on Wikipedia: http://www.quarry.nildram.co.uk/20mm1.jpg

Your casing appears to match the 20x110RB. None of the other casings have the same shallow shoulder that your does.

The only gun I could find that fired this round is here: http://en.wikipedia.org/wiki/Oerlikon_20_mm_cannon

That gun was used by U.S. Navy ships so it is possible your grandfather got a hold of one that way.

Also, from this page: http://cartridgecollectors.org/forum/viewtopic.php?t=1154&sid=76bd938fd2f62dde0e1f763da3b8903b

We find that the letter "B" in either a triangle or a circle is the headstamp of the "Bridgeport Brass Co., Bridgeport [CT], USA".

Hope that helps, you can probably do some more research on www.cartridgecollectors.org

Here's another page with a bunch of different cartridges including yours: http://www.quarry.nildram.co.uk/an_introduction_to_collecting_20.htm

**EDIT** One post I found on that site had this to say:

"Some collectors who are NOT familiar with the 20mm rounds may identify in a wrong way a 20mm fired shell case with the length of 110mm. As we can see in the table from above, there are 3 different 20mm rounds having the shell case 110mm tall: 20mm Oerlikon "S" with rebated rim [20X110RB], 20mm Hispano rimless [20X110] and 20mm US Navy rimless [20X110]. Measuring the rim diameter and observing the shell case shape and design, no mistake must be made when the 20mm shell case is 110mm tall. --- The article written by Tony Williams is excellent as usual, very nice work. Liviu 03/08/07"

That makes it pretty definitive that it is a 20x110RB.
 
The rebated rim shows that this is an Oerlikon case; this would've been fired out of one of these cannons, customarily mounted on navy ships for AA defense (in most footage of the "Kamikaze" attacks, you can see one or more of these, doing their best to knock the planes down before they can get close to the ships). At one point, the Germans used their OWN version of the Oerlikon in some of their fighters, but the case was shorter.

WNUS_2cm-70_pic2.jpg
 
I don't understand? Do you mean that this particular blowback action separated the forward part of the case mouth somehow, and this part was ejected separately?
 
What SDC means is that the neck of the case is not supported by the chamber when the gun fires, so is expanded through being fireformed. So although the case is all present, the neck of a fired case has a different shape from that of an unfired one.
 
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