Help in IDing this 20mm? cartridge

Looking for input on this cartridge.

Steel case, headstamp 2403 44 W9. Projectile measures 13.5mm at the red band, 12.8mm on the main body, and is stamped, eet 110/44.

TIA

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German 13x64mmB

Used in only one gun: the Rheinmetall-Borsig MG 131 aircraft machine gun of WW2.

That projectile is an armour-piercing incendiary.

Didn’t the Japanese have a percussion version of this too?

They did and so did Germany. Just the Japanese had problems in manufacturing electrical primers.

Elk suggests they were weary of electric primers in the humid tropics,i guess variable storage and potential reliability issues.