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Firing at different altitudes. VERY INTERESTING

2358 Views 12 Replies 9 Participants Last post by  iagbarrb
Hy folks!!

I was able to make a very interesting observation.

As you know, I live at 3600 m over sea level (about) 11.800 feet altitude.

I was in Miami last week, to make a course in medical devices. There was a colleague that lives in Miami that invited me to fire some rounds. We fired .22 9 mm and 45 ACP No rifles, just pistols.

I was surprised about the lower recoil from the pistol firing at sea level. It seems to be that the atmospheric density which is lower here in La Paz (680 mb against 1048 mb in Miami) makes the bullet faster and with more energy. Do you have some comments about this?

I also have to tell you have nice gun stores there in the US gents. I just was not able to walk out of the stores. AYAYAYAY. I suffered because I could not purchase a lot of things because I had not a license of our local ministry of defense to bring all the toys I would have purchased. I just purchased some cleaning stuff, and a chair. Next time, I will make all the paperwork needed for our customs, and bring some money to the US to clean out at least one store!!!!!!!!!!
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Instinct tells me you're right. I don't know if the science backs us up. Here in Santa Fe, the altitude is 7000 feet, and the relative humidity close to zero eight or nine months out of the year, so I'm guessing a higher atmospheric density (at lower altitude) and higher humidity (at sea level) would slow a bullet down. But to an appreciable difference a shooter would notice? You appeared to, so that's reasonable anecdotal evidence. I'd be curious to hear what some of the guys on the site more familiar with ballistics might tell us. Is a distance shot easier (meaning less variables) in La Paz than it is in Miami?
Chronographing bullets in Albuquerque, at 5950' above sea level and low humidity, I get much higher velocities than when I shoot the same bullets from the same guns back home in Indiana (630' above sea level, high humidity).

500-yard shots are easier here than at lower altitudes, because it's easier to see the target in the thinner, drier air. Don't know if the bullet travels better, but I sure hit better.
Lower air density means less air resistance/drag, means the rounds travel faster for longer, resulting in a flatter trajectory, particularly for flatpoint or round nose bullets. Also, the lower air density results in less atmospheric distortion when looking at a target. But I don't think that either of those would make a difference at handgun distances.
What I have to add, is that I had a better accuracy in Miami than in La Paz. I can imagine that the higher air density makes the bullet trajectory more stable, but it can also be that I was excited to be there with my old friends. ;)

The extreme altitude and atmospheric pressure as well as humidity difference between Miami and La Paz might make the difference appreciable to the shooter. But the lower recoil power in Miami was definitively noticeable. (I have not measured the bullet speed)

Anyway, I invite you to spend your holidays in my beautiful country and make your experiences. I will be happy to take you to our nice highest range in the world. You can use my guns.
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Humid air is generally less dense than dry air. A water molecule weights 18g/mol and air averages about 28g/mol. Alternatively, you need to get up to 18,000ft before the air pressure is half of that at sea level.
I also think that the most accurate shots would occur in low density air (ie close to a vacuum) where there is less stuff in the way to interfere. A projectile under water tends to yawl pretty quickly.
Ultimately I'm not sure where they would balance out, but it is an interesting question.

I'd love to shoot in a beautiful city like La Paz than in a Miami suburb, regardless of my accuracy or felt recoil though. :)
My 7mm 08 high power Silhouette rifle is pretty repeatable sight wise. We shoot at near sea level. When shooting the rifle and same loads at Raton NM about 5000 feet I need about 2 moa less sight elevation for 500 meter rams.

Not that that proves a thing as all rifle ranges are not the same distance. Few are measured accurately. However clearly the bullet is flying flatter at altitudes.

Let me add something.

We have started this year with high caliber Bench 300m. I am using a Mauser, open sights.
Last year we shot about 200m.
I thought I should target a tittle bit higher, but the bullets went over the target. To have better accuracy I had to shoot even lower than last year. And note, the Mauser is from factory prepared to fire straight at 300 m. Some comments?
I've never experienced altitude like what you live and target shoot in. So on that score, I don't know what to recommend.
If the rifle is hitting high at 300 meters, you may have to get a higher front sight post or barleycorn front sight so it will hit POA at the range you want. Perhaps more experienced and seasoned target shooters will have recommendations.


Military rifles with iron sights are not set up to hit bulls eye targets. The low or "Battle" sight setting is designed to put out a field of fire that relates to man sized targets for the longest possible distance. Example would be from Belt to Neck for a couple of hundred yards. Imagine a squad of riflemen shooting at advancing troops. They want the maximum number of hits.

When target shooting the old warhorses you need a higher front sight. Best make it way too high then file down to zero at some spot on the rear sight setting you can keep for reference. I don't know anything about Mausers but with US rifles the front sight blades are interchangeable and you can easily make a new one. My Trapdoor Springfields will take 03 Springfield blades that I file to zero at 100 when set at 200 on the rear sight. Have a 3x5 card that shows correct settings for other distances out to 1000 yards

Another easy dodge is to see how high the rifle hits at your chosen distance then set two targets, one to aim one to hit. All you have to do is set the aiming target up at the measured offset everytime. This is best for occasional use or a rifle you don't want to alter.

Altitude will make so little difference it's probably not measurable with service rifle iron sights. Not over a couple minutes of angle.

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As altitude increases, air density and drag decreases.This is why jets fly at such high altitude, they burn less fuel at high altitude than at sea level because the aircraft is pushing less dense air.

As to the increase in recoil, that is probably bc the lower atmospheric pressure is allowing the combustible gases to expand more violently. Two things will cause gas to expand: decreased pressure, and increased temperature.
I don't think the air pressure has much to do with the allowing more violent expansion. As I recall, SAAMI pressure for the 45 is 17,000 psi, which is one of the lower pressures in major calibers. Sea level pressure is 14.7 psi. Air pressure differences with altitude are miniscule compared to the cartridge's pressure.

Edit: 17K psi is .38 spec, .45 ACP is 21K.
It seems to be that expansion is more violent. And catrige pressure is not the only issue. Density of air is important, as well as the air pressure against the end of the barrel and air pressure in the whole barrel lenghth.
We were douing some calculations at the university, and believe it or not, air pressure and air density are very important even it air pressure differences with altitude are miniscule compared to catridge's pressure.
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