Handloads at higher altitudes

DaneN · September 22, 2005, 11:58 PM

I've got a load for my 308 that uses 46.4 grains of IMR 4895 behind a 150 grain spire point. Its the maximum recommended load in the Hornady 5th edition for the round, but I get terrific accuracy and muzzle velocity.

I'll get an opportunity to go elk hunting at about 8000 feet in Colorado; my current altitude is around 500 feet. I'm a little worried about chamber pressure due to the altitude change, and was wondering if anyone knew how the pressure effects the round and if I should compensate for it.

I looked online but couldn't find any way to figure out what the change will be. I can get a muzzle reading up there and re-calculate the ballistics, I'm more worried about the chamber pressure.

Thanks in advance.

mete · September 23, 2005, 01:28 AM

I don't ever remember seeing data on altitude/pressure . There is data on temperature vs pressure and velocity therefore loads should be developed in the summer and they will be safe in the winter.

MADISON · September 23, 2005, 07:22 AM

High Altitude...Lower temperature?
Wouldn't that fall under the "temperature" rule?
If wou work up a load in the winder, it will probablly be "too hot" in June or July. You can work up a load in the heat of the summer and it will not shoot the same in the winter.

Foxman · September 23, 2005, 12:26 PM

The air pressure and density is lower so it should go a few fps faster, other wise it shouldnt be an issue.

DaneN · September 23, 2005, 01:31 PM

Thanks everyone, I worked this up in the Texas summer and will shoot it in the Colorado winter. It sounds like the pressure will be fine but I might lose a few fps due to temp and gain some due to air pressure.

Morgan · September 24, 2005, 04:37 PM

There was a good article on this in Front Sight not long ago.

Volume 22, No. 4, July/August 2005. See The Chronoman Report: Elevation and Velocity, page 18.

The quick and dirty is that most loads have higher velocity at higher elevation.

30Cal · September 26, 2005, 10:23 AM

It will shoot somewhat higher due to lower air density. Chamber pressure isn't an issue though.

Crosshair · September 26, 2005, 02:29 PM

Yea, chamber pressure is going to be OK, you are only loosing a few PSI at 8000 vs 500 ft. Compare that to the 50,000+ PSI that a 308 generates. It is not going to be an issue. Now for the big question, what about a gun in space?

Cowled_Wolfe · September 26, 2005, 05:57 PM

Quote:

Now for the big question, what about a gun in space?

Atmosphere: 14PSI.
.308: 50,000PSI.
.308 in space: 49,986PSI.

No appreciable bullet drop, no bullet deceleration. Poke a hole and Mr. Target is a goner. Recoil might suck though.

As a very off topic thought... Sabots would rule the day. Ultra-high-velocity, low-lead-time rounds... Just gotta poke that hole in Mr. Target.

On the other hand, temperatures vary wildly in space so you might have issues there...

Wolfe... (Sorry 'bout the thread hijacking; carry on.)

Crosshair · September 26, 2005, 09:27 PM

Ya, nothing to worry about with velocity in space, but wow is Mr. Newton going to have fun with you.

September 22, 2005, 11:58 PM	#1
DaneN Junior Member Join Date: September 19, 2005 Location: College Station, TX Posts: 4	Handloads at higher altitudes I've got a load for my 308 that uses 46.4 grains of IMR 4895 behind a 150 grain spire point. Its the maximum recommended load in the Hornady 5th edition for the round, but I get terrific accuracy and muzzle velocity. I'll get an opportunity to go elk hunting at about 8000 feet in Colorado; my current altitude is around 500 feet. I'm a little worried about chamber pressure due to the altitude change, and was wondering if anyone knew how the pressure effects the round and if I should compensate for it. I looked online but couldn't find any way to figure out what the change will be. I can get a muzzle reading up there and re-calculate the ballistics, I'm more worried about the chamber pressure. Thanks in advance.

September 23, 2005, 07:22 AM	#3
MADISON Senior Member Join Date: January 1, 2000 Location: Roanoke, Virginia Posts: 2,678	high altitudes High Altitude...Lower temperature? Wouldn't that fall under the "temperature" rule? If wou work up a load in the winder, it will probablly be "too hot" in June or July. You can work up a load in the heat of the summer and it will not shoot the same in the winter.

September 23, 2005, 12:26 PM	#4
Foxman Senior Member Join Date: August 13, 2005 Posts: 466	High altitude The air pressure and density is lower so it should go a few fps faster, other wise it shouldnt be an issue.

September 23, 2005, 01:28 AM	#2
mete Senior Member Join Date: June 14, 2004 Location: NY State Posts: 6,575	I don't ever remember seeing data on altitude/pressure . There is data on temperature vs pressure and velocity therefore loads should be developed in the summer and they will be safe in the winter.

September 23, 2005, 01:31 PM	#5
DaneN Junior Member Join Date: September 19, 2005 Location: College Station, TX Posts: 4	Thanks everyone, I worked this up in the Texas summer and will shoot it in the Colorado winter. It sounds like the pressure will be fine but I might lose a few fps due to temp and gain some due to air pressure.

September 24, 2005, 04:37 PM	#6
Morgan Senior Member Join Date: October 29, 1998 Posts: 945	There was a good article on this in Front Sight not long ago. Volume 22, No. 4, July/August 2005. See The Chronoman Report: Elevation and Velocity, page 18. The quick and dirty is that most loads have higher velocity at higher elevation.

September 26, 2005, 10:23 AM	#7
30Cal Senior Member Join Date: December 3, 2002 Posts: 1,264	It will shoot somewhat higher due to lower air density. Chamber pressure isn't an issue though.

September 26, 2005, 02:29 PM	#8
Crosshair Senior Member Join Date: December 16, 2004 Location: Grand Forks, ND Posts: 5,333	Yea, chamber pressure is going to be OK, you are only loosing a few PSI at 8000 vs 500 ft. Compare that to the 50,000+ PSI that a 308 generates. It is not going to be an issue. Now for the big question, what about a gun in space?

September 26, 2005, 09:27 PM	#10
Crosshair Senior Member Join Date: December 16, 2004 Location: Grand Forks, ND Posts: 5,333	Ya, nothing to worry about with velocity in space, but wow is Mr. Newton going to have fun with you.