US Primer, Percussion, M1, M1A1, M1B1, M1B1A1, M1B1A2
This primer is used with the normal charge in the 75mm gun shrapnel round. It is a 100 grain primer. The head is similar to that of the M22 Primer and the brass flash tube is a drawn brass case open at one end, the other end being slotted to receive a screwdriver.
This primer has been modified on three different occasions. The B1 modification consists of a change in the flash tube. The redesigned tube is made of brass tubing closed at the one end by a threaded brass plug, roll-crimped in place. This change was made to aid procurement, some manufacturers being equipped for drawing operations and others for tubing operations.
The A1 modification is similar to that of the M22A1 Primer.
The A2 modification is similar to that of the M22A3 Primers.
The present standard 100-grain primer is designated the M1B1A2.