Interesting thoughts on a springer losing power by higher altitudes?

[45flint]

I was searching the internet for a airgun issue and ran across this posted on this forum in 2003. Not sure unless you live in the high mountains it makes a difference but it's something I never thought of?

"Crosmans are designed to cope with the wide variations in altitude and climate in the U.S. A brass gun will not rust in the dampness of the east coast. A spring rifle, when shot at high altitudes, loses 2% of its power for each 1000 ft. above sea level. I often hunt at 10,000 feet above sea level, which means that a springer expressing 12 ft-lbs at sea level will produce 9.6 ft-lbs at my hunting ground. A pneumatic or CO2 gun will perform the same at any altitude."

[Benelli B76]

I was searching the internet for a airgun issue and ran across this posted on this forum in 2003. Not sure unless you live in the high mountains it makes a difference but it's something I never thought of?

"Crosmans are designed to cope with the wide variations in altitude and climate in the U.S. A brass gun will not rust in the dampness of the east coast. A spring rifle, when shot at high altitudes, loses 2% of its power for each 1000 ft. above sea level. I often hunt at 10,000 feet above sea level, which means that a springer expressing 12 ft-lbs at sea level will produce 9.6 ft-lbs at my hunting ground. A pneumatic or CO2 gun will perform the same at any altitude."

Surprised that the the thinner air the pellet has to push through does not compensate for the lower pressure in the chamber. The reason aircraft fly at high altitude there is less air resistance.

Baz

[Mr. Gen]

Surprised that the the thinner air the pellet has to push through does not compensate for the lower pressure in the chamber. The reason aircraft fly at high altitude there is less air resistance.

Baz

less air compressed during the firing cycle? My initial thought was that it would have thought it would have been relative but as there is an exponential element to the conversation of potential energy to kinetic energy then possibly not although I'm not sure the 2% is either accurate or relevant.

[Airsporterman]

Something to do with the quality (denseness) of the air in the piston/spring rifle at different altitudes, as said - air/oxygen gets thinner with altitude.
PCPs uses compressed air - the quality of the 'charge' will remain more or less 'constant' at different altitudes!

something on those lines I suspect, all other things being equal!

ASM

[45flint]

Not sure all that is interesting is relevant? Lol I would assume you would have to pump a pneumatic more times as well? Would assume in US this would be easy to test if the above figures are accurate? If you live in Denver "the mile high city" your springer would change from when you vacationed at the beach, or when you lived on the coast? As anal as high end air gunners are hard to believe no one ever noticed? Of course the math above could be bogus?

[air-tech]

Don't know the maths but this here is very interesting: https://www.mide.com/pages/air-press...ude-calculator

Taking 3000m (10000ft nom) elevation, psi drops from almost 15 at sea level to almost 10. Very substantial.

The mass of air for a set volume (cylinder volume ahead of cocked piston) would also drop substantially too.

[draitzer]

There are loads of posts on the Yellow Forum about this topic - search for "altitude" and scan thru the results. As others have said, because spring guns have less mass of air to compress they'll slow down as elevation increases; pump-ups require more strokes to charge with the same mass of air at higher altitude; while CO2 and pre-charge will dispense the same actual charge of gas regardless of altitude. In all cases there would be a small velocity increase effect from the reduced pellet drag.

Don R.

[Mr. Gen]

Something to do with the quality (denseness) of the air in the piston/spring rifle at different altitudes, as said - air/oxygen gets thinner with altitude.
PCPs uses compressed air - the quality of the 'charge' will remain more or less 'constant' at different altitudes!

something on those lines I suspect, all other things being equal!

ASM

Not at all - with a pcp the power will increase with elevation as the air pressure drops.

[air-tech]

Not at all - with a pcp the power will increase with elevation as the air pressure drops.

Technically correct but possibly unmeasurably or insignificantly?

If you refer to the fact that on the exhaust side of things you may have 10psi rather than 15psi opposing the exit of HP air - that would be a difference of 5psi opposing 1500 psi (100 bar nom) so percentually the drop is very very small.

There would also be less mass of air in the barrel ahead of the pellet to be shoved out but the significance would have to be calculated, but in any case this applies to all guns not just PCPs so is not really in the scope.

Unless I am missing something?

[Turnup]

An airgun has to push the pellet and the air inside the barrel out.

Assume a 0.22 barrel 30 cm long. It contains just under 7 grams of air at STP and at 10 psi about 4.5 grams of air. A difference of 3.5 grams - which is 54 grains! If I have done my sums correctly this is a significant difference in the effective weight of the pellet. Of course the air in front of the pellet is not a deadweight, it is compressible so the effect is not as strong as these numbers would suggest but I would expect a certainly measurable increase in Me for a PCP operating at 10,000 feet over the same at seal level.

Better set those PCPs to 6 ft-lb in case a zealous forensics department tests your gun at 10,000 feet altitude and declares it capable of producing over 12 ft-lb

And you springer users can't relax either. It works the other way around - testing in Death Valley will increase the Me

EDIT: This is garbage as correctly pointed out by airtech below - ignore.

[air-tech]

Whoa, maths.

5.6mm bore

24.63 sq mm

7389 cu mm barrel volume = 7.389 cu cm


Mass of air at 20C = 1.2041 kg/m3 (1000000 cu cm)

Mass per cu cm = 1204 (gr) / 1M = 0.001204 g/cu cm

7.389 x 0.001204 = 0.008896356 grams of air in barrel size quoted

[Turnup]

Whoa, maths.

5.6mm bore

24.63 sq mm

7389 cu mm barrel volume = 7.389 cu cm


Mass of air at 20C = 1.2041 kg/m3 (1000000 cu cm)

Mass per cu cm = 1204 (gr) / 1M = 0.001204 g/cu cm

7.389 x 0.001204 = 0.008896356 grams of air in barrel size quoted

Ahem.........you are of course correct and I was spouting complete bx (in haste for my tea ready on table but this is no excuse). The effect is negligible. Thanks for checking.