
The Cartridge, HEI, Mk 1, w/Fuze, Percussion, DA, No. 253 Mk. I /A/, was adopted from the British in 1941. Little modification has followed except in the redesign of the cartridge case and primer. The fuzed projectile remains the same as may be sensed from the adopted British nomenclature. (/A/ is the British symbol for shell used in aircraft mounted guns.)
No information about hazardous components.
OP 1664, Volume 1 - US Explosive Ordnance (1947)
TM 9-1904, Ammunition Inspection Guide (1944)