Use of personal firearms in every theater I was deployed to was strictly forbidden. For one thing, its a violation of ITARS. in some units, its even forbidden for personnel to use personal accessories like forward grips, optics, etc. That said, it was normal practice in MY unit to re-purpose captured weapons of all types to friendly indigenous forces, and in some cases press them into service ourselves (depending on the weapon type/purpose, serviceability, etc.) But, bringing your own Kimber desert warrior or Glock 17C with meprolight sights that you purchased stateside on a blue label deal was very unauthorized and I would have never done such a thing.