I thought of the SCUBA tank because, a.) I have one. b.), when my dad still coached the OSU pistol team, he used the dive shop my wife and I were using (gone now) to refill the reserve-size tank the team refilled their compressed air pistol cylinders from. I made an adapter on my lathe for him for the hoses that came with the guns. I've forgotten what we had to adapt. Probably for a metric hose thread.