
This projectile is an Army design manufactured for the Navy to Naval specifications.
The AP round has a plug in the tracer cavity; the AP-T has a red tracer.
The M81 cartridge differs from the M81A1 in that its windshield is attached to the projectile body by an adapter.
No information about functioning.
Nothing else to see.
OP 1664, Volume 1 - US Explosive Ordnance (1947)