Helium anyone using??

[Stubbers]

Wouldn't ya need to tether your rifle so it doesn't float away when left on the bench....JK!

The 2200~ or so fps shots done by a couple GTA members were with very light pellets, I don't recall the exact weight but say a 1.9 gr projectile going 2200 fps is only 20 fpe.

-Matt

 

[TheBeardedGunsmith]

That calculator was likely written to model systems that were well below choked (sonic) flow velocity. Since it does not take into account those limitations, the results fall apart at anything close to what we see in an airgun. That calculator is probably only taking friction losses into account. By entering very large pipe diameters, with a very short length, I was able to get that calculator to display air flow velocities that exceeded the speed of light. Most of us would agree that is not possible.

Mass flow rate becomes choked at the speed of sound. Though peak velocity can be higher than that since the air can also be expanding as it is flowing. The maximum velocity front ends up being about 2x the speed of sound of the propelling air.

Mach velocity in helium is much higher than air, so it would have a higher velocity limit. But it’s main advantage in an airgun is it’s much lower mass. In higher power airguns, the mass of the propelling air can exceed that of the projectile, even at speeds as low as 950fps.

I thought the same as well and wasn't even going to build the 50 caliber rifle that I did because I thought I would be limited by the laws of physics until I was set straight by a friend of mine, a mechanical engineer that retired from a nuclear power plant that designs steam flow systems. Air flow in our airguns are not in any way limited to the speed of sound comparable to that of a gas expanding from deflagration or detonation due to having its own fuel and oxidizer. They just aren't related. That calculator uses a principle that takes into account for gases being released at whatever pressure you type in and I assume it's based off of a principle or equation of physics, although it doesn't account for coefficient of friction. My airgun pushes 325 grain slugs at 1587fps which wouldn't be possible if you were right.

 

[Scotchmo]

…. My airgun pushes 325 grain slugs at 1587fps which wouldn't be possible if you were right.

And I’ve shot very light slugs at about 1800fps. Both 1587fps and 1800fps are significantly below 2x the speed of sound. So where did I say that wouldn’t be possible?

FYI: That Copely velocity calculator will show unrealistic (impossible) results if applied to an airgun. Don’t use it for that purpose.

Edit: 1587fps is possible. I’m not saying that I believe/disbelieve your 1587fps with a 325gr slug in a 26” barrel. Not enough information to make that call.

 

[Badgerfarm]

Check out some of Mr Hollowpoints videos as he does a lot of testing with helium in his big bore air rifles. I've never found the need for it in any of my big bore air rifles. The cost doesn't justify it for me. My 2 cents.

 

[Exodus]

When I decided I was going full on eye ball deep in PCP Airguns, I decided nitrogen was the way to go. I’m an HVAC tech and use nitrogen to purge and pressure my HVAC refrigeration lines, so it’s easy to obtain and relatively cheap to use. Where I live, high pressure tanks aren’t a thing so I have to rely on 2400psi tanks. My fix was to give low pressure supply air to my compressor and pump it into my tank. I can’t say that this is a 100% nitrogen charge in my SCBA tank, but probably a 95% or better straight nitrogen. I did however in my adventures look into using helium because a lot of bid bore guys were using it. The expansion rate is considerably higher than air or nitrogen. But the take away is most of those rifles don’t use regulators. And I was advised that some regulators will NOT regulate helium. So it’s possible to over pressure your gun. And from what I had researched, FX rifles will break using helium because of design. So just something to think about.

As for nitrogen, I like it. No moisture, that’s its biggest and best feature.