Elevation change from 2,000 feet to 7,400 feet

[ballisticdaddy]

I have a few rifles that I shoot f-class matches with in southern California averaging about 2,000 feet above sea level. Just moved to Colorado and my current location is now 7,400 feet above sea level. I am curious as to how much load tweaking will be needed with the +5,000 feet increase in elevation? Any useful information would be greatly appreciated.

 

[Turbulent Turtle]

I'm not sure why you think your load will need tweaking.

Your trajectory table may need to be touched up and JBM will do a great job for that.

 

[ballisticdaddy]

I'm not sure why you think your load will need tweaking.

Your trajectory table may need to be touched up and JBM will do a great job for that.

I had imagined the burn rate would be different with the gain in elevation and I do use JBM for my trajectory so that I was not too worried about....thanks Denys

 

[nmkid]

When we moved from NM to VA we went from around 5K to 186' above sea level. All I had to do was sight in again and everything was good.

 

[Turbulent Turtle]

I had imagined the burn rate would be different with the gain in elevation and I do use JBM for my trajectory so that I was not too worried about....thanks Denys

Internal ballistics will be the same. Once the bullet leaves the bore, that can change slightly.

 

[Dusty Stevens]

Your load needs to be changed if you shot in the same place a month later. If youre good to go at the lower elev all it may take is seating depth tweak anyway

 

[Flouncer]

Plug it in to JBM. What happens to "match" factory ammo in the same scenario ??

 

[LoganDon]

Our range in Kingman, AZ is around 2k feet and I hunt Idaho at 7k+. My biggest change is temperature, 100 degrees to 30-40 degrees but have recently switched to a less temperature sensitive powder, H4350 and things seem to be virtually the same. I am within 1" at 100yd with the altitude change.

 

[1shot]

I'm in Ohio at 1,200' ASL. Went to Colorado at 5,500 ASL and shot some of my best scores. What I did find is the my 9 twist 7mm. barrel w/184 SMK's shot just OK in Ohio but was a laser in Colorado. The same thing happened in the reverse a couple of months ago. My 6SLR with a 7.5 twist shoots great at my home range. Went to St. Louis with an elevation of 575 ASL and both score and X count dropped off.
The moral of the story is have enough twist for the lowest elevation you shoot, or go with a lighter bullet.
I hope this helps,


Lloyd

 

[Liven The Dream]

I live at 4000 ft. El. to all my loading at 4000 .
I shoot mostly Palma and travel. I shoot northern Cal. and Raton NM to Arizona .

At Raton NM with a .308 Palma Rifle 7600 ft. El. your 1000 yard El. setting is your 900 yard setting for other places.
Your load is the same. 300 to 800 yards are off a little.

Good luck in your New Home.

 

[ballisticxlr]

I find that every ~1000ft of elevation is worth 10deg Fahrenheit of air temperature. That works for me very well as far as I go with it which is +/- 3000ft from my baseline. How much of an effect there will be really depends on the aerodynamic efficiency of the projectile. Flat shooting fast 6's with BC's over 600 don't see nearly as much of a delta compared to a .308 with 168's with BC's under 450 in play.

Here's a comparison between a 6XC with 115's from sea level to 7500ft to a .308 with 168's
.
.308 @ 7500ft .308 @ sea level

At 1000yrds at 80F the difference is 1.2mil which is pretty huge.

Then looking at a 6XC.

6xc @ 7500ft 6xc @ sea level.

The difference at 1000yrds at 80F is only half a mil. Still enough for a miss on a pretty big target but nothing like the .308's delta.

Hope that helps.

 

[Dusty Stevens]

I'm in Ohio at 1,200' ASL. Went to Colorado at 5,500 ASL and shot some of my best scores. What I did find is the my 9 twist 7mm. barrel w/184 SMK's shot just OK in Ohio but was a laser in Colorado. The same thing happened in the reverse a couple of months ago. My 6SLR with a 7.5 twist shoots great at my home range. Went to St. Louis with an elevation of 575 ASL and both score and X count dropped off.
The moral of the story is have enough twist for the lowest elevation you shoot, or go with a lighter bullet.
I hope this helps,


Lloyd

Dont you think your load was marginal and the change of elev either brought it in or took it out? Its just like some br competitors that shoot the same load all year- you can follow their scores to see when the load comes and goes. Most times they blame it on a bad day

 

[1shot]

Dusty,
I thought about that, but the 7mm never shot great. Ok, but not great. As a high master shooter, when my X count is consistently below 30% something else is going on. I assure you it wasn't for a lack of tuning or load development on my part. To take the same load to a higher elevation and have it perform dramatically better really opened my eyes. When I got back home, I screwed on an 8.25 twist that I had waiting in the wings and the rifle started performing great. 50-67% X counts became the norm using the same load.This example coupled with my 6SLR that is my "go to" 600 yd. rifle behaved the same way when going from 1,200 to 575 ASL. I'm sure I wasn't having a bad day when I grabbed my back up rifle a BRX shooting Roy Hunter bullets and promptly cleaned the next match. (200-8x)
On the plus side, I got some of Bart's Gungnir 105's and they are showing great promise in the development I did yesterday.
I hope this helps,

Lloyd

 

[Bindi2]

It is purely barrel harmonics for me.
I get it going from sea level to just over 500m, others blow primers and some rifles perform better. Purely the load being used outside of were it was developed.

 

[D-4297]

Higher altitude means less density , and usually lower humidity = less drag on your bullet . Your zero will change , and you won't have to make as large a come-up to reach the same known distance . As long as you aren't loading on the edge of total destruction , your load should be okay . If you are , I'd suggest re-calibrating the load down-wards of 15% and work it back up . I have a 95% load I use at 1,200 - 1,500 MSL that I have shot at 8,300 MSL with no negative effects ...so far .

 

[284winner]

I have a few rifles that I shoot f-class matches with in southern California averaging about 2,000 feet above sea level. Just moved to Colorado and my current location is now 7,400 feet above sea level. I am curious as to how much load tweaking will be needed with the +5,000 feet increase in elevation? Any useful information would be greatly appreciated.

You'll need quite a bit less elevation. You'll get a bunch more free velocity as well. If your looking for the same drop at the higher elevation, you will need to change your load. Not sure why you'd want to do that tho. Take the advantage of less drop and better ballistics. It's a favor in wind.

 

[JFrank]

Dont you think your load was marginal and the change of elev either brought it in or took it out? Its just like some br competitors that shoot the same load all year- you can follow their scores to see when the load comes and goes. Most times they blame it on a bad day

start a database, I’ll bet that would interesting.

 

[mikecr]

Higher altitude means less density , and usually lower humidity = less drag on your bullet.

You're backwards on relative humidity. Lower humidity = higher drag. Also shifts MACH, which shifts the drag curves taken w/respect.

OP, don't assume altitude in itself affects either internal or external ballistics.
The parameters in play are Temp/Abs Press/Rh, regardless of altitude.
For internal, temperature can matter depending on your management of it. We don't know what efforts you've made there.

 

[Turbulent Turtle]

You're backwards on relative humidity. Lower humidity = higher drag. Also shifts MACH, which shifts the drag curves taken w/respect.

OP, don't assume altitude in itself affects either internal or external ballistics.
The parameters in play are Temp/Abs Press/Rh, regardless of altitude.
For internal, temperature can matter depending on your management of it. We don't know what efforts you've made there.

You are very correct on higher humidity, lower drag. Air is ~78% nitrogen (atomic weight of about 14, molecular weight of 28), ~21% oxygen (atomic weight of 16, molecular weight of 32) and about ~1% of argon (atomic weight of 40) and traces of CO2 and water vapor and other stuff.

Water is composed of 2 hydrogen (atomic weight of 1) and 1 oxygen (atomic weight of 16). So as you can see water vapor (molecular weight of 18) is very light, which is why we can sleep peacefully at night as we don't get brutally woken up by the sound of clouds crashing to the ground.

The only real thing that affects the Mach number is temperature; humidity has a very small effect in it.

So, when it's hot and sticky outside, your bullets fly faster and the Mach number is higher, but planes have more difficulty getting lift. Conversely, when it's cold and dry the bullets go slower, the Mach number is lower, but planes take off faster and easier.

 

[searcher]

As other noted - your load will probably remain accurate - but you will need to tweak your drops. I have two drop charts for each of my heavily-used varmint rifles as my primary shooting location is 300 ft. elev. and my second is 4,400 ft. Using the wrong chart will result in a squirrel-sized miss at distance.