Old wives' tale. All weapons the US uses in war are good to go on all legal targets. IOW if you see a lawful or unlawful combatant direct or indirect fire with any US weapon is legal IAW LOAC.
Maybe that was just something they told them to get them to shoot at the belt buckle, which is where you want to aim anyway.
In addition to which I misidentified this as 50 Caliber.
It was actually!
http://www.navweaps.com/Weapons/WNUS_16-50_mk7.php
Lone Palm I stand corrected!
WWG1WGA
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
Xone..hold on! My source, Sgt. Susie was NOT an old wife at the time, although she is by now. (Trying to recall if she had her tongue in her cheek...)
Anyway, good to know that taking off your canteen and web belt won’t keep one from being targeted by the US Military!