Help Identifying 20mm Round

Hello, my boss recently liquidated his militaria collection and gave me this 20mm projectile. He believes he bought it decades ago at an Army/Navy Surplus but isn’t sure. No identifying markings that I can see to make this easy. Solid brass band at the bottom. My best guess is a target practice dummy for a vulcan but I think it’s too old to be that. Any ideas?

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looks like ones Ive seen from vulcan M56 ammo. Dummy with fuze? inert M56 more likely. WW2 projectiles Ive seen had brass fuses vs Steel or Aluminum.

Thanks for the reply! Yeah the base is solid, same kind of rusty color. Nothing drilled out unfortunately which would settle issue of being inert. Know of any identifiers that signal it being inert? My worry is that the primer is intact, since my boss’s recollection is of buying it decades ago, that’s a pretty shaky provenance.

Photo of base:


Sectioned TP round showing the aluminum nose plug.

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Are there any markings on the driving band?

None that are easily visible. Later tonight I’ll break out the magnifying glass and a brighter light just to make sure there weren’t any that faded.

Close up of the nose if it helps.

The thing is now that there are 3 different calibers possible.
20x110 USN
20x110 HS

Can you put a cal. .50 round next to it and do a side shot at 90° so no distortion will influence the ID?

`Sure! Posted below:

It looks much like the by Brian above said 20x102 TP.

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Oh well that’s a relief. Boss couldn’t remember exactly where his brother got it sometime in the 1960’s. Wanted to make doubly sure I didn’t have an HEI round sitting in the house.

All I saw in Picture was the projectile. Was there also a case? projectile may be inert but I don’t know how to tell. I have some practice 20mm that are painted blue. The projectile you showed is typical of a 20mm M56 projectile with a nose cap. Most of them have solid bottoms. I acquired a few intact but inert projectiles whenI worked for the army. The loaded rounds would have a HE projectile or every so often a tracer. I dont (usually) collect above 50 cal because of the chance they are explosive. Of Course there are a variety of rifle/MG caliber rounds that are explosive so Maybe I shouldnt have been worried. Sorry I cant help more. John Guenther . .

All good. I honestly never collect ordnance, just got saddled with it; will be getting rid of it when I can. No casing, boss’s brother had it for decades in a desk drawer then gave it to him in the 80’s.