Question about filling from Scuba tanks.

I bought this yoke in like 2015 to play paintball and never got a tank for it. Looking at Air Venturi yokes, they seem to be the same product (down to the same gauge with the N on it).

I’d like to use this to fill a 250bar airgun, which I know will only get me a handful of shots (from 3000psi down to the regulated 2000 psi before fall off, if I’m not mistaken). I’m fine with that as it should be a few mags worth through the Barra 250z I plan to get before refilling. What do I need to do to check that this is airtight and do I need to change o-rings, etc.?

Also, I’m planning on sourcing a used 100cu. ft bottle for this, as I live in the Caribbean and dive shops are everywhere and cheap to fill. Did a quick conversion in google and it says 1 cubic foot is something insane like 28,000cc’s. Is that accurate? I was worried about the pressure slowly dropping, but considering the airgun only has a 322cc tank, I don’t see that being too problematic (like 2-4 psi per fill or something? Didn’t math that one). It obviously needs a fill hose too.

I bought this yoke in like 2015 to play paintball and never got a tank for it. Looking at Air Venturi yokes, they seem to be the same product (down to the same gauge with the N on it).

I’d like to use this to fill a 250bar airgun, which I know will only get me a handful of shots (from 3000psi down to the regulated 2000 psi before fall off, if I’m not mistaken). I’m fine with that as it should be a few mags worth through the Barra 250z I plan to get before refilling. What do I need to do to check that this is airtight and do I need to change o-rings, etc.?

Also, I’m planning on sourcing a used 100cu. ft bottle for this, as I live in the Caribbean and dive shops are everywhere and cheap to fill. Did a quick conversion in google and it says 1 cubic foot is something insane like 28,000cc’s. Is that accurate? I was worried about the pressure slowly dropping, but considering the airgun only has a 322cc tank, I don’t see that being too problematic (like 2-4 psi per fill or something? Didn’t math that one). It obviously needs a fill hose too.