Nathan works in places where explosive weaponry doesn't work, I recall?

Perhaps a pneumatic rifle would be an interesting idea. They enjoyed a brief period of popularity before being eclipsed by improved conventional guns. Not little BB gun toys - those things were used in real war. They are also quiet, no muzzle flash, stealthy, and can fire successive shots with a delay of only seconds - at least until the tank is empty and needs pumping up again.