What is this 5.56x45mm round?




Well, I found out what it is.

It is a “Brass Standard” - a round used to validate the gage and weigh system that throws out UNDERWEIGHT rounds during the mfg process. It is filled with inert powder 60% weight… also an inert primer with inert primer mix in the cup and an anvil, the projectile is the correct component for M855…

The GB number is the Blue Print number for that GAGE round, the S number is the GAGE SET…
There are 25 of these in a set, the coating on the brass is black oxide and the text is machine engraved.