Shooting at altitude

by B.B. Pelletier

I recently spoke to a disgruntled airgunner about how he hated spring-piston guns. He was fed up with them! They never lived up to their advertising. In the course of the conversation he happened to mention that he lives at 10,400 ft. altitude.

Problem solved!
Of course his springers don’t perform! At that altitude, they can’t get enough air to compress, and no amount of wishing can change that fact.

Testing airguns at altitude
Over the years, several tests of different airgun powerplants have been performed at varying altitudes. The best one I have seen, though it was a short one, was done by Howard Montgomery, the owner of Reno Airguns. It was published in The Airgun Letter in 1996. Howard tested several springers, CO2 guns and multi-pump pneumatics from sea level to 8,500 feet. He found that springers became weaker (shoot slower) with altitude, but it’s hardly noticeable until you get above 2,000 feet. CO2 guns become more powerful (shoot faster) as the altitude increases, and multi-pump pneumatics get weaker.

Springers die when you go high!
Howard’s test ended at a lower altitude than the man I spoke to. I would guess that his springers would lose up to 40 percent of their rated power at the higher altitude. Howard also reported that his more powerful spring guns (an RWS 36 and a Gamo 2000, which is no longer made) were making horrible sounds above 6,500 feet. That’s probably because there wasn’t enough air to cushion the piston when it went forward.

CO2 gets faster, but there is a catch!
Less air means less resistance to a pellet in flight. Hence, faster speed from a gas gun. Unfortunately, the higher you go, the greater the chance the weather will be cool, and CO2 dies in cool weather. So, indoors at altitude, yes – outdoors (most of the time) – no.

When the air is rare, multi-pumps have nothing to compress
Multi-pumps got slower as the altitude increased. There is less air for them to compress and store. That could be offset by pumping more strokes to compensate, but Howard stuck to the owner’s manual.

PCPs rule!
Howard didn’t test them, but PCPs will dominate at altitude. A PCP is less affected by cold than any other powerplant, and a PCP stores compressed air at a constant pressure. The combination of lower air pressure outside and constant pressure in the reservoir means that a PCP will just get faster as the altitude increases. This could be offset if the gun has been lubricated with oil or grease, and the temperature goes VERY low. Also, low temperatures cause a drop in air pressure inside the reservoir – just not the great drop we see in CO2.

So, for high places, the PCP is the powerplant to choose. If you go with a multi-pump, you’ll have to experiment on how many extra strokes to give it.

19 Responses to “Shooting at altitude”

  • turtle Says:

    Well now there you go again.

    living in the north east and vacationing in upper Maine, NY, and New Hampshire. That puts springers completly out of my air gunning picture.

    Now, since it seems air shotguns don’t have the power to bust a clay pidgeon!?! I gotta ask will putting multiple lead balls down a high quality rifled barrel ruin it for pellet accuracy?

    I’m asking cause I’m guessing about three would weigh around the same as a kodiac pellet and sight similar at mid-ranges. Some get up to 22.0 grains in the last lot I got. The idea comes from wads I saw while surfing to keep them in place till shot. and it would be fun to check the patterns… but not at the cost of a L.-wather barrel!

  • Denny Says:

    Turtle. Using a Sheridan, i tried using two pellets at a time. One always printed much lower than the other. I also tried a pellet followed by several BB’s with about the same results.
    I’m wondering if a gelatin capsul filled with small lead shot, small enough to fit the breech without rupturing would blow apart as it is fired and thus spread the shot?

  • Earl Cox Says:

    Thanks for the info on the scope I mounted on the RWS 52. Made the changes and it cured the problem is shooting 1.5 groups at 35 yards.
    Earl

  • turtle Says:

    Thanx Denny, always looking for a new angle. Sounds like it may be a waste of ammo. Just curious what gun were you trying. As it turns out the guns I’m shooting a talon and ss are adjustable and can be set to blowout so much more air than needed any single pellet can use, I thought it may be strong enough to group when cranked way up. Gotta wait for BB’s input on tearing up the barrel though. $150 is a big replacment cost if I mess it up.

  • B.B. Pelletier Says:

    Turtle,

    Two lead pellets in a barrel should do no harm. Steel BBs would ruin a rifled bore unless the gun were made to shoot them, of course.

    You might try two lead balls, too. They wouldn’t hurt the bore and might fly better than stacked pellets. At any rate the experiment would do no harm to your gun as long as they are lead.

    More than two and you might have a problem closing the gun’s valve. You could dump an entire tank with one shot. Not harmful but a pain.

    B.B.

  • B.B. Pelletier Says:

    Earl,

    Great! Now we are making progress. How is that trigger coming?

    B.B.

  • B.B. Pelletier Says:

    Turtle,

    I’ve only covered one air shotgun thus far. Be patient. There is one that will bust a clay pidgeon.

    B.B.

  • turtle Says:

    Ha, now that would be blowing out alot of air…I’m trying to follow the thought on air flow….soooo, if I were to try this out with a ton of wieght, I’d close down the talons valve more and start w/ a medium power wheel setting working up for effect.

    I really want to try this!!! Even if ya only get 5 to ten hunting shots from a tank, in a “survival scenario” it would pack a whollup with a good chance of a hit when your body isn’t at full funtion…if they group.

    thanks yet again, looking forward to the other shotguns!

    Turtle

  • turtle Says:

    Just had a thought that if you Really, really, wanted a pump and were dedicated to the effort ya may be able to rig something similar to a torque wrench as the pump arm to be used as a pressure guide…hmmm maybe a guaged pump gun is the ticket…

  • B.B. Pelletier Says:

    Turtle,

    A “gauged” pump has been built. In fact, I’ve tested them. Multi-pump pneumatics are bad for the UK, where they can exceed 12 foot-pounds, so British designers and others who want to import to the UK put blow-off valves in their compression chambers.

    Like the release valve on a pressure cooker, they open whenever the internal pressure reaches the level at which 12 foot-pounds can be generated.

    When you pump the gun the pump arm lets go suddenly, smashing your fingers against the stock.

    B.B.

  • turtle Says:

    ….so much to learn! A valve like that is the perfect solution.

  • Mike Says:

    B.B.

    I bought a Diana 34 a month ago, and the main spring is already broken. I live at 8400 feet, and I am concerned that this gun will eat springs here. I love it otherwise, and hope there is some solution.

    Mike in Colorado

  • B.B. Pelletier Says:

    Mike,

    I think you may be right, however there may be a solution. Jim Maccari may be able to supply you with a mainspring that will take the stress better than the factory spring. Google him and see if he can help.

    B.B.

  • Anonymous Says:

    BB.
    I live at 7500 feet and i have a Daisy multipump that works very well, will a springer such as a a HW77 not work at this altitude?

    Thanks
    Will

  • B.B. Pelletier Says:

    Will,

    It won’t work very well. There’s not enough air to cushion the piston. You’ll lose between 30% and 40% at that altitude.

    B.B>

  • Anonymous Says:

    BB.
    What about a single stroke pneumatic such as a Baikal 46M, will it work at around 7000 feet?
    Will

  • B.B. Pelletier Says:

    Altitude,

    Not very well.

    B.B.

  • Anonymous Says:

    I wonder if you were able to close the transfer port hole up a bit if it would compensate for the thin air. I dont think you would get the power back but it may help the spring life by providing more resistance for the piston.

  • B.B. Pelletier Says:

    Transfer port,

    What you suggest sounds interesting. I did the reverse of your test, by opening the transfer port wider on a Beeman R1. After 0.125″ no more velocity was gained.

    B.B.

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