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Brian Enos's Forums... Maku mozo!

Elevation affect on velocity


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Can anyone tell me what affect elevation has on velocity? I'm in Albuquerque, just over a mile high

I bet I'd have to re-sight my rifle in if I were hunting

(wish I were) in Albuquerque - especially for long range


Bet there's not too much effect on handgun rounds at 20 - 30 yds



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Elevation DOES change MV very slightly. Humidity more so. At higher elevations, not only is the density less, but the partial pressures are also reduced. These minor effects essentially result in the column of mass in the bore in front of the bullet weighing less. The resultant ejecta (Powder mass + bullet mass + column mass) is therefore lighter at altitude (humidity being same grains of water/pound of air, not RH). Doing testing between 10, 8, 5 and 1 thousand feet...with an auto-pistol, the variation will likely be within your statistical error range, given equal grains of water per pound of air. With a rifle (.30-06) the variation is enough to affect MV very slightly.

Once you leave the muzzle and get to exterior ballistics, air viscosity (water, density are dominant variables) is typically less at higher elevations than at lower elevations. Some people who are concerned with the effect will use "Density Altitude" which is a number used in aviation, to figure out if the changes are significant enough to be worried about. For a .223, out to 200 yards or so, they are insignificant to a 1MOA rifle. By the time you get to 500 yards, the changes could be in excess of 1 MOA. There have been times, when at 5K feet, I have measured DA to be as low as 3200 feet and as high as 9900 feet.

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Thank you for the good answers. What other factors should one consider when loading rounds that will be shot in a different location? IE I'm loading in Albuquerque and I will be shooting in St George UT for Area 1. Want to make sure that what I get from the chrono here is at least close to what I'll get there.

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For pistol, my above discussion boils down to...It does not matter.

For where you are to UT, give yourself a comfortable cushion and call it good. Most people will suggest 3 to 5 points above required PF. If Minor, I go for 135. In major, would suggest 168 at a minimum.

Temp has some affect on powders, but again, not a bunch. There are some good threads here on suggested PF levels to make sure and meet Chrono, even for specific loads. I'm pretty sure after posting 165, 165 and 166 at my last three majors, I stressed out more of my squadmates than myself at Chrono. :surprise:

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I live in ABQ, I shoot in AZ. OK, and NV. My loads using VV320 show almost no difference in PF from these locations.

The heat may affect your load. Some powders are sensitive to heat. You might want to check that part out first.

I was at Nationals in OK. I shot both matches, the same ammo had a 4 PF difference when the rounds were quite cold. Still made major.

Edited by pjb45
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