[Railgun]

For actual playing I would strongly suggest you do not run the full 3000'ish tank pressure through a remote hose. If it ever gets torn loose or the line eventually weakens from kinks and other normal wear and the line breaks then a 3000 psi jet of air coming out of the line or fitting will be quite capable of serious harm injury or even death. 3000 psi is not something to fool with.

Assuming you're using one of the smaller pony bottle setups on your back I would suggest you set up the arrangement mentioned above where you plumb a paintball tank reg to the output from the scuba bottle. Or if by some chance the scuba bottle uses the same threads as the existing tank threads just replace the scuba valve with the paintball reg directly. Alternately I would look at getting a paintball reg modified to fit onto a scuba tank yoke so it fits directly onto the valve much like the regular scuba first stage reg does. That by far would be the cleanest installation. And that way the tank can be easily filled by any regular scuba shop.

The scuba first stages are set typically to 150 psi. Or at least they were back when I was actively diving and paid attention to this sort of stuff. New ones may be using 125psi like you guys are saying. They are adjustable but I seriously doubt that they are adjustable over enough range to hit 700 to 850 since there is just no need for them to vary over that sort of range. Scuba regs also use Oring sealed fittings rather than tapered pipe fittings like paintball is used to using so there's no way to use our regular stuff on any scuba regs without some serious modifications.

Now if you're talking about using a full on 80cu ft scuba tank then you're obviously in far, far better shape than I'm in since my 80 weighs around 40 lbs when filled and mounted in the backpack. One of the 20 cu ft bottles wouldn't be bad but they are still quite the load to pack if you're a run and gun sort of player.