(from http://www.atf.treas.gov/pub/fire-explo_pub/gca.htm)
The term "semiautomatic assault weapon" means - a semiautomatic rifle that has an ability to accept a detachable
magazine and has at least 2 of --
(1) a folding or telescoping stock;
(2) a pistol grip that protrudes conspicuously beneath the action of the weapon;
(3) a bayonet mount;
(4) a flash suppressor or threaded barrel designed to accommodate a flash suppressor; and
(5) a grenade launcher;
That means if it is a POSTBAN receiver with detachable magazine you can have only one of these features. If you have a pistol grip, you can't legally have a flash hider or threaded muzzle too, or you have an illegal "semiautomatic assault weapon". If you have a preban receiver you are good to go.
Also, if it is a postban, just by having the flash hider on same premesis as the rifle with a threaded barrel, there could be a violation according to [18 U. S. C. 921( a)( 30)] which states: "Semiautomatic assault weapons in knockdown (disassembled) condition consisting of a receiver and all parts needed to assemble a complete semiautomatic assault weapon are subject to regulation if the parts are segregated or packaged together and held by a person as the parts for the assembly of a particular firearm." This would be subject to interpretation by the BATF.
The fact that you are in the military makes no difference, unless you are specifically authorized by your Unit Commander to carry personally provided weapons. I know of few military units which allow this, except possibly Delta Force type units and special Military Police units. It could be a court martial offense for a soldier to carry an unauthorized personal weapon, and that's not even considering whether or not it is in banned configuration. Civilian LEOs who are active in a law enforcement agency can legally own a semiautomatic assult weapon, but must relinquish or modify it if they are no longer employed by the LE agency. Anyone please correct me if I have said something innaccurate, but I believe this to be the case.
It's none of my business what you do, I just would hate to see anyone get burned because of ignorance of the current complicated firearms laws and regs. Any of these offenses could result in a felony conviction, which would prevent an individual from ever legally owning or purchasing a firearm again. Something to think about for sure.