Thoses dents could happen from the brass tumbeling around in the big bins at the factory, the only way to tell is if there are any marks on the exstractor area on the brass.
And marks there and its a dead give away, that's said if its mil brass then most of it will have been shot via a BMG and you will see faint ring marks 1/2 way up the body from the links.
The brass most likely was intended form Mil contracts that's been canceled, so who knows?
bbb