HPA from Scuba tank Many questions

[SeanMP]

I think the link I posted was for a 62ci. That's what I bought in the past from Eric.

Of course the caveat being the gun I use with that bottle is tuned to shoot target. If you amp it up to a hot hunting rifle you will get less.

[pharoah007]

I think the link I posted was for a 62ci. That's what I bought in the past from Eric.

Of course the caveat being the gun I use with that bottle is tuned to shoot target. If you amp it up to a hot hunting rifle you will get less.

Aah.. I did not pick up on the linked bottle being the 500 shot Reference.

Ballpark approximation of how many shots to a hunting tune ?

What is the diff between the tunes in terms of regulated pressure at bottle and fps from rifle ? (Qb78 .22 context )

, thanks

[SeanMP]

Generally speaking the regulated pressure stays the same regardless of the tune on the rifle. The higher the pressure the more efficient the gun will be. The QB tube has a max working pressure of 1600 psi so you set your regulator to that and tune around it by changing the spring load and port restriction.
I think Todd just posted that with a simple spring adjuster he was able to adjust from 350fps to about 900fps

The easiest way to figure out roughly how many shots you will get is to use an arbitrary efficiency number
Typical efficiency numbers range from 1.1fpe per cubic inch of air for a hunting tune to 1.8fpe per cubic inch of air for a target tune (calculated at 1 atmosphere-1bar)

So you'll be shooting from 3000psi (200bar) down to 1000psi (70bar) giving you a usable range of 130bar

Thus a 62cubic inch tank times 130 = 8060cu/in of usable air

A respectable hunting tune in 22cal is 20fpe

So for a hunting tune

(usable air) times (efficiency) divide (energy) = number of shots

8060air x 1.1efficiency / 20fpe = 443 shots


And for a field target tune

8060air x 1.6efficiency / 12fpe = 1074 shots

And a 10m target/plinking tune

8060air x 1.8efficiency / 8fpe = 1813 shots

Does that clear things up?

[pharoah007]

Awesome, detailed reply. Thanks!

As for spring, I assume we are talking about the hammer spring, correct?

Stiffer hammer spring = more HPA being let out of valve = higher velocity and FPE.... all at the expense of the valve stem (does this sound right?)