Socket identification found on plane crash

[NANDRIN]

 

[herman1rg]

Looks to me like a 20mm shell case, but i'm not an expert.

 

[Wurger]

Yes, that's the base of of the 20mm cartrige around primer pocket made in 1942. The F.CO. abbreviation is the manufacturer's initials ( headstamp ) and may indicate the Frost & Co, Kenosha, Wis., USA.

 

[special ed]

Also, the triangular crimp marks at the primer indicate it was a reload. Recovered brass was reloaded once and used in gunnery training, not for combat.