40MM Headstamp

[Dunkbfg]

40MM US bofors casing with FA that looks to be Frankford Arsenal, but was expecting M25 as the type designation.
Can anyone hazard a guess as to what the MI/L means? I'll try to get a better idea of the primer type when this arrives.

Many thanks for looking.

Duncan.

 

[HAZORD]

The 40mm Bofors gun was first obtained for evaluation in the U.S. in 1940. The Army designation for the gun was M1. At first the U.S. used British projectiles and ammo, before they adopted it and started to produce their own. They also had to use British Imperial dimensioned drawings because the Swedish drawings were metric. Even though the gun is referred to as L60 to represent a barrel 60 calibers long, in actuality the barrel is 56 calibers long. Frankford Arsenal in the U.S. is known for producing prototype and experimental ammunition, until the ammo is type classified as standard, where it is assigned a model number (M) for Army ammo or (Mk.) for Navy.

Since 1942 is so early in the production cycle, it is my theory that your headstamp M1 designates it for the single barrel Army gun, followed by the /L with no number for caliber because the caliber was confusing (56 versus 60). Just a WAG.