Pretty good website below for cartouches:

http://www.trfindley.com/pgsnstmpsm1.html

Scroll down to the HRA section and according to this website:

S/N 4,661,000 to 5,609,000
Department of Defense Acceptance Stamp, 3/8" by 3/8" on left side of stock. The other stamp used was the circle 'P' proof mark, without serifs.

__________________________________________________ _______

S/N 5,561,000 to end of production
Department of Defense Acceptance Stamp, 1/2" by 1/2" on left side of stock. The other stamp used was the circle 'P' proof mark, without serifs.


Hope that helps nail it down...
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