Stagarms makes a great AR15 rifle. The guns come very accurate out of thhe box. However, they are very tight actions so you may encounter some feeding issues with cheap steel ammo early on. I had this problem, but after about 500 rds of brass ammo thru it I had no problems with the steel.
I have the Stag mod 1 A2 style with a 16" bull barrel, and I couldn't ask for a better rifle.
As far as the corps goes, I am just a civvie. Can't tell you a thing that you probably don't already know.
Thank you for considering service.