Hmmmm. Wish I knew. I know that I have seen many a pistol brought back that would NOT meet the GCA68 criteria. I think that if you buy one over there while in the Military and ship it back with household goods, it's not considered importing it. Might be wrong on this as I've only gotten it second-hand. As it is, I've got Friends overseas I'm hitting up to do just that. Asking the BATF is a lost cause, they always say no.
Normally, you'd have to fill out a BATF Form-6 or something like that. This is for importing firearms. BATF will deny it if it doesn't meet their standards. If, however, you are purchasing a firearm and then storing it in the armory while stationed there you'd just be shipping it with your household goods back to the states. Interesting if the loophole would work.