If you want to be extra obnoxious ... you can upcharge for "vacuum-rated" weapons that are designed and tested to fire in zero pressure
This would include use of different lubricants, for example, that are not prone to vacuum-welding due to out-gassing and such.
Also, keep in mind the thermals - does the ammunition work at those temperatures?
Finally, if it's a "smart" slug thrower - are the electronics hardened for direct exposure?
Most electrolytic capacitors are not going to fare well... many solder joints won't either.
Does the battery leak and explode in zero pressure or low temperature?
Look into what it takes for even the simplest items to get qualified for use in orbit by NASA, ESA, Roscosmos, etc. pressure, temperature, radiation - all of these have to be accounted for ... part by part.
- some of the NASA standards for inspecting electronics are terrifying compared to what I see in commercial / home use hardware.
Given what it takes to get a groundside laptop qualified to work in orbit on the space station, 5 X to 10 X base price of a groundside piece of equipment doesn't seem unreasonable...
We live, as we dream -- alone. ~ Joseph Conrad