What is it?

Yesterday, recycling parcs opened again, thank you, corona. Shortly after, this fella landed on my desk.

Not on the pictures is the inscription on the driving band: 1943 37 mm M63 mod1 E n-1-56. There came a lot of black moisture out of the case between casemouth and projectile. And what happened to the primer? To me, the whole seems original. According to some documentation, Ammunition Inspection Guide of March 1944, this should be a practice round, filled with sand for the one pounder, the M1916. But I read something of a practice, filled with black powder too? So before I put it in quarantine, can someone id the whole thoroughly?

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Maybe a close relative? 37x145mmR "37mm Mark III A2 Lot 6574-5 C.B.& C. Co.1941"

No relation to the 37mm aircraft gun round.

This should be a subcaliber round!
And a very nice one btw!


This one normally has a black powder filler but when it is leaking out I assume it was submerged for some time.

Image from:
TM 43-0001-28, Artillery Ammunition Data Sheets, 1994


Here is a scan from TM 9-1901, 1950:

The M63A1 TP shell is the same as the M63 HE used in 37 mm cartridges (37x222R) for M6 guns, but filled with black powder instead of TNT. Base fuze is the same (M58).

It was used in subcalibers for 37 mm Model 1916, M12, M13 and M15 guns, and also 90 mm M1 and M1A1 in Anti-Motor Torpedo Boat mount only.

The case was manufactured by Frost Co., Kenosha, Wisconsin, and the M23A1 primer by Picatinny Arsenal, Dover, New Jersey.