Regarding the “bringing your own gat to the fight” notion… I know for a fact many an aircrew who felt it prudent to stash a favorite large caliber pistol in his gear on short Dets, though prohibited for a myriad of reasons. Primarily that most Unit or Squadron / MAG / WING / MEF… whoever’s policies forbid personal weapons, since we all have our t/o pistols and rifles issued. In Iraq it is absolutely impractical and also against the regs to bring your own stuff. How am I going to hide my HK USP for six months, while openly carrying my M9…? What’s the point? And then, while in my world we fly ourselves back home in our aircraft, and the customs guys might search one out of 30 sea bags as a random measure when we get back to the USA, but if you are “that guy” whose .357 falls out… oopsie. But come or go via CAM flight, and they go through all your crap usually. Hide it in gear being loaded; you are taking your fate in your own hands…
So it really isn’t a BATF issue but more a culmination of various DoD/service regs.
Regarding bringing stuff back, that is a combo of BATF and DoD policies, though most likely not intentionally. There are very specific guidelines regarding what you can bring home “legally”. Under than falls the prohibition on arms (that are functional). If you pull off an AK barrel to bring home, I doubt anyone will note the current barrel importation ban, but who knows. You could find a nice AK stock to add to your collection… maybe a bayonet, dust cover, whatever. The odd one'sies and two'sies. But too much of that sort of thing attracts attention. And there are concrete theater rules from the JAG on what you can legally bring home and can’t. I keep trying to sneak all the parts to a nice Chinese F7 (MIG 21 copy) into the back of my Herc. There are so many of them in almost not totally shot up condition that I could frankenstein one into a totally functional aircraft, and other semi-complete former Iraqi aircraft lying all over the place here. But it is getting conspicuous having that jet’s fuselage and wings under my mattress…
That article amuses me though. I am yet to see 50 round MP5 mags. Maybe they exist. I am no expert by far on the matter but own a bunch of 30 round mags, and maybe there are some odd contract 40 round MP5 mags.