Helium instead of HPA

[Eljefe13]

Has anyone had experience with helium instead of HPA? My latest homemade air rifle was already performing pretty well with HPA (38 FPE).
Then I tried helium and it increased to 53 fpe!!!
Apart from the cost, are there any other down sides to using helium?

[jackssmirkingrevenge]

Helium is a smaller molecule than Nitrogen or Carbon Dioxide and therefore often has problems with sealing system made for air, but aside from this, the cost and the dangers of a hilarious death if firing repeatedly in a confined space, no other downsides

[Air2theBrain]

Any chance of a video with you speaking whilst shooting it?

http://www.spudfiles.com/pneumatic-cann ... 26691.html

[Eljefe13]

Helium is a smaller molecule than Nitrogen or Carbon Dioxide and therefore often has problems with sealing system made for air, but aside from this, the cost and the dangers of a hilarious death if firing repeatedly in a confined space, no other downsides

Yes I already knew about it being more likely to leak compared to HPA but haven't had that problem yet, I made the valve stem out of hardened tool steel and delrin after many failed attempts using rubber o-rings.

I've also heard that it is less likely to create valve lock compared to HPA.
Also heard that it performs at a less efficient rate than HPA so it might turn out to be too expensive to continue with it.

[Eljefe13]

Any chance of a video with you speaking whilst shooting it?

http://www.spudfiles.com/pneumatic-cann ... 26691.html

Haven't got any videos yet but plan to do a couple in the near future, got a few pics though so I'll try and upload them.

[D_Hall]

Helium is a smaller molecule than Nitrogen or Carbon Dioxide and therefore often has problems with sealing system made for air, but aside from this, the cost and the dangers of a hilarious death if firing repeatedly in a confined space, no other downsides

OP,

In addition to what JSR said...

There are some advantages, to using helium... The smaller molecule means better flow under choked conditions. This means that if the performance of a gun is being dominated by the (lack of) performance of an undersized valve, helium can significantly improve performance as you noted.

HOWEVER....

Unless your gun is shooting near sonic conditions for the gas in question (ie, Mach 1 for air), this should not be an issue. If it *IS* an issue, it is a sign that your valve has been poorly designed. A better solution than using helium would be to redesign the valve.

[Eljefe13]

Helium is a smaller molecule than Nitrogen or Carbon Dioxide and therefore often has problems with sealing system made for air, but aside from this, the cost and the dangers of a hilarious death if firing repeatedly in a confined space, no other downsides

OP,

In addition to what JSR said...

There are some advantages, to using helium... The smaller molecule means better flow under choked conditions. This means that if the performance of a gun is being dominated by the (lack of) performance of an undersized valve, helium can significantly improve performance as you noted.

HOWEVER....

Unless your gun is shooting near sonic conditions for the gas in question (ie, Mach 1 for air), this should not be an issue. If it *IS* an issue, it is a sign that your valve has been poorly designed. A better solution than using helium would be to redesign the valve.

Cheers for the advice, yeah I get what you're saying but I'm pretty sure choking won't be a problem.
I've designed the valve and stem a bit large if anything so the only drawback would be decreased shot count.
Which is something I'll gladly give up in exchange for more power.

[D_Hall]

What are your muzzle velocities?

[Eljefe13]

What are your muzzle velocities?

At 2000 psi I'm getting 1150 fps.
Might try 2500 and then 3000 today and see how it goes.

Pic attached.

[Eljefe13]

Best so far is 1198 fps for a total of 58 foot pounds @ 2500 psi from a .22 18.13gr pellet.

Groupings of half inch @ 25 metres.

[Air2theBrain]

Chrono pics please

How long is your barrel?

[Eljefe13]

Chrono pics please

How long is your barrel?

Just got 1320 fps when shooting a 19.09gr pellet.
73.88 foot pounds.

24" barrel.

[Air2theBrain]

Nice..so that fps was achieved with a 2000psi shot of air?

[Eljefe13]

Nice..so that fps was achieved with a 2000psi shot of air?

The gauge was sitting on about 2,200 psi of Helium.

[jackssmirkingrevenge]

That must make quite a crack! Interesting rifle build, I'm guessing it's a home made hammer valve?