Reloading & Altitude ---

GoldenRoyBoy · December 31, 2008, 01:29 PM

Here's something most people, including myself probably never thought about; altitude, and how it effects reloading/shooting.

My wife and I moved to Trinidad, Colorado over two years ago. We'd lived in Texas too long; never adapting to the hot summers there. Anyway, Trinidad's altitude is approximately 6200 feet. We live twelve miles west, upon a mountain top. Our altitude is approximately 6700 feet. Several months ago, I got back into reloading/shooting; having done it for a number of years, back in East Texas. Right off the bat, everything I had loaded before was shooting hot! I thought time had somehow played a part. Wrong. After pulling almost all my old stock, I began reloading again; but, useing the same specs as before with the same hot results! It did not take me long to figure out I had to reduce my powder charge, in most cases by a whopping 25%! That's a lot; but I'm certainly glad I didn't have to go the other direction. As we all know, powder is expensive.

Here's an example; showing a new load I worked up for 45acp. Hornady's book; their 6th Edition, Page 832 suggest, using a 230g LRN, Clay Universal Powder for 750-fps-5.2g--800-fps-5.6g. COL is 1.245. Up on top my mountain, 5.2g pushes, a hot 911-fps; as verified through my Pro-Chrono Chrony!. I reduced downwards; settling on 4.3grains, hand measured through my RCBS ChargeMaster 1500. My average speed, using hand casted 230g LRN Moly coated, & Moly lubed is a good, safe shooting 816-fps! Oh, the things we learn!!

Good shooting!
GRB

PCJim · December 31, 2008, 02:14 PM

Golden, you're describing the same effect as baseball players have found when playing at Coors Field. The less dense atsmosphere allows the ball players to hit longer home runs. I suppose you've discovered that is also allows for higher velocities. I'd be curious as to what your chrono is indicating for factory ammo as a comparative.

rwilson452 · December 31, 2008, 02:58 PM

Your load was likely still at safe pressures but due to the less dense atmosphere it was going faster.

**Shane Tuttle** · December 31, 2008, 05:15 PM

Do you have other negative indicators such as case split, flattened primers, etc?

I know the altitude difference you're talking about. But, I'm not so sure that you're loading beyond max pressures....

DaveBeal · December 31, 2008, 05:46 PM

According to this calculator, the air density at 6700' is 22% less than at sea level, given the same temperature, barometric pressure and humidity. Aerodynamic drag is proportional to air density (at least it is for subsonic airplanes; I assume its effect on subsonic bullets is similar), so it makes sense that you're getting substantially greater velocities downrange. However, I would expect that the velocity at the muzzle would not be significantly different than at sea level.

I'm not a reloader or ballistics expert, but I don't see why it would be unsafe to use the same loads at sea level and at 6700'. Yes, there's a few pounds per square inch less atmospheric pressure pushing inward on the chamber, but that's negligable compared to the many thousands of PSI developed by the powder.

Welcome to Colorado, GRB!

GoldenRoyBoy · January 1, 2009, 11:08 AM

Hello Guys!
Thanks for the responses!

Yes, altitude definitely effects both powder ignition, and bullet speed. Also, altitude does effect this shooter's felt recoil. So, IMO it's not only the bullet traveling faster. I shoot a lot; consequently, I have developed both an ear and a touch for such. I did have some brass damage. Whether the two cases, out of 50 or so were damaged by excessive pressure, age, or feeding into the chamber is hard to tell. I suspect a combination of all three factors. However, my primers did buckle and flatten, depending on the handgun I was shooting at the time. I tend to shoot multiple guns of the same caliber when I shoot. In this instance, 45acp. So, I'd rather err on the side of safety; reducing my loads substantially. Besides, IMMHO there's no need to load any 45acp round much faster than 800fps as long as the semi-auto's action works properly. At least, the 230 grain lead round nose I'm casting.

Yes, even factory loads are faster. At least the Federal 223's I shot were; averaging several hundred fps faster than I recall the same bullet's velocity back in East Texas. Also, I recently acquired a Savage 99 in 243. Man, those Hornady suckers zip!

Enjoy your holidays!
GRB

.

**Shane Tuttle** · January 1, 2009, 11:24 AM

It's good to see that you're taking safe measures in reloading. However, I do caution you to not get too overzealous on backing off your charge.

Too LOW of a charge is sometimes just as, if not, more dangerous.

December 31, 2008, 01:29 PM	#1
GoldenRoyBoy Junior member Join Date: November 10, 2008 Location: Trinidad, Colorado Posts: 107	Reloading & Altitude --- Here's something most people, including myself probably never thought about; altitude, and how it effects reloading/shooting. My wife and I moved to Trinidad, Colorado over two years ago. We'd lived in Texas too long; never adapting to the hot summers there. Anyway, Trinidad's altitude is approximately 6200 feet. We live twelve miles west, upon a mountain top. Our altitude is approximately 6700 feet. Several months ago, I got back into reloading/shooting; having done it for a number of years, back in East Texas. Right off the bat, everything I had loaded before was shooting hot! I thought time had somehow played a part. Wrong. After pulling almost all my old stock, I began reloading again; but, useing the same specs as before with the same hot results! It did not take me long to figure out I had to reduce my powder charge, in most cases by a whopping 25%! That's a lot; but I'm certainly glad I didn't have to go the other direction. As we all know, powder is expensive. Here's an example; showing a new load I worked up for 45acp. Hornady's book; their 6th Edition, Page 832 suggest, using a 230g LRN, Clay Universal Powder for 750-fps-5.2g--800-fps-5.6g. COL is 1.245. Up on top my mountain, 5.2g pushes, a hot 911-fps; as verified through my Pro-Chrono Chrony!. I reduced downwards; settling on 4.3grains, hand measured through my RCBS ChargeMaster 1500. My average speed, using hand casted 230g LRN Moly coated, & Moly lubed is a good, safe shooting 816-fps! Oh, the things we learn!! Good shooting! GRB Last edited by GoldenRoyBoy; December 31, 2008 at 01:36 PM. Reason: correction

December 31, 2008, 05:15 PM	#4
Shane Tuttle Staff Join Date: November 28, 2005 Location: Montana Posts: 9,443	Do you have other negative indicators such as case split, flattened primers, etc? I know the altitude difference you're talking about. But, I'm not so sure that you're loading beyond max pressures.... __________________ If it were up to me, the word "got" would be deleted from the English language. Posting and YOU: http://www.albinoblacksheep.com/flash/posting

December 31, 2008, 05:46 PM	#5
DaveBeal Senior Member Join Date: January 16, 2008 Location: Colorado Posts: 158	According to this calculator, the air density at 6700' is 22% less than at sea level, given the same temperature, barometric pressure and humidity. Aerodynamic drag is proportional to air density (at least it is for subsonic airplanes; I assume its effect on subsonic bullets is similar), so it makes sense that you're getting substantially greater velocities downrange. However, I would expect that the velocity at the muzzle would not be significantly different than at sea level. I'm not a reloader or ballistics expert, but I don't see why it would be unsafe to use the same loads at sea level and at 6700'. Yes, there's a few pounds per square inch less atmospheric pressure pushing inward on the chamber, but that's negligable compared to the many thousands of PSI developed by the powder. Welcome to Colorado, GRB! Last edited by DaveBeal; December 31, 2008 at 05:54 PM.

January 1, 2009, 11:08 AM	#6
GoldenRoyBoy Junior member Join Date: November 10, 2008 Location: Trinidad, Colorado Posts: 107	Good New Year's morning! Hello Guys! Thanks for the responses! Yes, altitude definitely effects both powder ignition, and bullet speed. Also, altitude does effect this shooter's felt recoil. So, IMO it's not only the bullet traveling faster. I shoot a lot; consequently, I have developed both an ear and a touch for such. I did have some brass damage. Whether the two cases, out of 50 or so were damaged by excessive pressure, age, or feeding into the chamber is hard to tell. I suspect a combination of all three factors. However, my primers did buckle and flatten, depending on the handgun I was shooting at the time. I tend to shoot multiple guns of the same caliber when I shoot. In this instance, 45acp. So, I'd rather err on the side of safety; reducing my loads substantially. Besides, IMMHO there's no need to load any 45acp round much faster than 800fps as long as the semi-auto's action works properly. At least, the 230 grain lead round nose I'm casting. Yes, even factory loads are faster. At least the Federal 223's I shot were; averaging several hundred fps faster than I recall the same bullet's velocity back in East Texas. Also, I recently acquired a Savage 99 in 243. Man, those Hornady suckers zip! Enjoy your holidays! GRB . Last edited by GoldenRoyBoy; January 1, 2009 at 11:20 AM. Reason: Correction

January 1, 2009, 11:24 AM	#7
Shane Tuttle Staff Join Date: November 28, 2005 Location: Montana Posts: 9,443	It's good to see that you're taking safe measures in reloading. However, I do caution you to not get too overzealous on backing off your charge. Too LOW of a charge is sometimes just as, if not, more dangerous. __________________ If it were up to me, the word "got" would be deleted from the English language. Posting and YOU: http://www.albinoblacksheep.com/flash/posting

December 31, 2008, 02:14 PM	#2
PCJim Senior Member Join Date: July 11, 2008 Location: FL Posts: 570	Golden, you're describing the same effect as baseball players have found when playing at Coors Field. The less dense atsmosphere allows the ball players to hit longer home runs. I suppose you've discovered that is also allows for higher velocities. I'd be curious as to what your chrono is indicating for factory ammo as a comparative.

December 31, 2008, 02:58 PM	#3
rwilson452 Senior Member Join Date: June 10, 2004 Location: Tioga co. PA Posts: 2,647	Your load was likely still at safe pressures but due to the less dense atmosphere it was going faster.