US Cartridge, 20mm AP-T, M75
This cartridge is used primarily from aircraft against the armored parts of other aircraft, and may also be used against lightly armored ground and sea-borne targets.
The “T” in the nomenclature of this round stands for tracer mixture which is charged into the cavity in the base of the projectile. After the tracer charge is loaded, it is sealed by the assembly of a celluloid closing cup held in place by an adhesive compound.
Nothing else to see.
Collaborative Ordnance Data Repository