Are nitrogen paintball tanks refillable

Answer 1

High pressure air, and all air for that matter, is about 78 percent nitrogen, so it is nicknamed a "nitrogen tank" . So a HPA tank is supposed to be filled with "nitrogen" which is really just air.

Answer 2

Absolutely! And are by far easier to fill than CO2 from a Ref's point of view. just make sure you know how much to fill it, otherwise, you top will blow off.