I took an expended Nitrogen cylinder and modified it to make it refillable using standard air. A simple mod: drilled and tapped the end for 1/4npt screwed in a 1/4 to 18 npt adapter and welded it in. I had a steel street tee and screwed that into the cylinder using Loctite 569. I bought a miniature 0-5000 psi gauge from McM-Carr and a fill fitting (w/ checkvalve) from airtanksplus. Right now I'm doing a leak-down test as, with great effort, I managed to hand-pump it up to 3600 psi. The only thing I don't like about it is that I have to remove the fill fitting if I want to remove it and use the N2 cylinders, because it would hit the barrel otherwise. The nitrogen cylinders come filled to 3600 psi, so I don't believe there are any safety issues. All the fittings are good to 5000 psi plus. Total cost ~ $45.00 less the expended N2 cylinder. Should make plinking a little less costly.
