It's Cal, short for Caliber, and using a K instead of the C just makes you sound like an idiot. And the Halo 3 Pistol fires a 12.7mm (which does convert to .50 Caliber, but its measured differently for a reason) round. However, being that they are military workers (it's generally assumed that the Voi Traxus plant they seem to work for was producing something for the war effort) its likely that they were actually trained in the use of small arms, at very least. It really has nothing to do with their ethnicity- American or not.