Powder charge & elevation....or something

[Roger B]

So here is something that I ran into last month at the Western Rondy.  I used my .54 Douglas 1 in 48 barrel in a "long range shoot" (actually appx. 100yds) & my usual Oklahoma charge of 80grs FFFg shot about 3" low & not particularly "tight".  Remembering a similar experience from about 8yrs ago in WY, I started bumping the charge until I got to 95 grs & everything got back to normal.  Even won the match.  The Wy experience was much the same, but with a .58 cal DeHaas barrel 1 in 72".  Is there something about going from the hot, humid, flatlands to the hot, dry, great basin that should effect the elevation & grouping?
Roger B.

[Sam Everly]

Elevation , how much higher or lower the shooting range has a lot to do with it . I ran in to that a couple of years ago shooting on top of a mountain in Western NC, "Catalooche log shoot" I shot about 1 1/2 inches higher on top of the mountain . I don't know how much differance the elevation was but i think it was 1000 to 1500 feet .   

[Daryl]

Gosh Sam- didn't know we lived on top of amountain. Our city elevation here is 2,000' and the range is about 2,300'ASL.  Actually, we live on a pretty flat plain, with the mountains around us to the East going up from here - snow-capped year around.

Increased or decreased elevation certainly plays a part in changing a ball or bullet's elevation on the target, that's for sure.

[Sam Everly]

Yea , elevation changes alot of things . In my line of work "Racing" where you race relates to your jetting ot the engine.The closer you get to sea leval the bigger jet or more fuel you have to add. 

[BrownBear]

I'm well acquainted with the process for centerfire rifles, but hadn't considered that it might (and probably logically, too) be more extreme for muzzleloaders.  With CF rifles there are changes in trajectory, but it takes a lot of elevation change to cause the kind of differences you cite.  With the slower and less airworthy projectives from MLs, it only makes sense that they would be affected more, especially as range stretches and velocity gets really low.  While I've hunted as high as 12,000 feet with a CF rifle, my top with a ML is only about 2,300 feet.  I'm sighting and doing most of my shooting at sea level, BTW.  Since I rarely shoot more than about 50 yards with a ML by choice, I haven't noticed any change between 0 and 2,300 feet.

But based on your reports, I'll be watching for significant change in trajectory if I start pushing 100 yards or beyond.  I'm not likely to shoot so far, but you've provided very useful info for  my "data base."

[Candle Snuffer]

It's a fact, it does change.  When moving to NW Nebraska from Ohio about 20 years ago, I went from shooting at an elevation (in Ohio) of 860' above sea-level, to (Nebraska) 3900+ feet above sea-level...  Had to make sight adjustments to all my muzzle loaders.

Now when I go from NW Nebraska to Cental Nebraska for State shoot I have to adjust again because I'm dropping from near 4000' to 1500'....

That's why I finally went with the adustable Bo-Mar rear sight on my serious competition rifles.  I was getting smoked big time by relying on
kentucky windage (but more importantly) elevation.  Last year I finished
fourth in State.  I think it was the right sight move to make.

[Roger B]

It must be something beyond round ball ballistics, though I realize that ballistics is an important factor.  I say this because down here in OK, the particular barrel in question doesn't seem to burn more than 80grs of FFFg at max.  You can add more powder, but you quickly get much more recoil & no trajectory rise.  In WY, that same barrel ate another 15grs with favorable results on target.  Is there a difference in rate of powder burn with elevation or decrease in humidity?
Roger B.

[William Worth]

It was running rich due to altitude.

[Burgess_rudy]

Yes, less oxygen. The higher in elevation the less oxygen there is. That is what causes high altitude sickness. Less oxygen means poor burning performance. Although humans can adapt over time by producing more red blood cells in the body to make up for the deficiency, that all depends on how high you are.

Also, it is a law of physics that large objects create their own gravity. Higher elevations tends to mean mountains and a large force that may act upon the gravitation pull against the ball in flight.

Air density affects trajectory too:


http://www.longrangebpcr.com/Accuracy.htm

So all of them can be acting upon the trajectory, but it is most likely the density and lower oxygen levels that are critical to burn the powder.

[BrownBear]

It would be really interesting to chrono the same loads at high and low elevations.

[William Worth]

Actually, oxygen concentration stays the same at altitude but the oxygen pressure drops.  In a human, that results in less oxygen being driven across the lung membranes into us.  In an engine, there is less pressure to feed the combustion process.  Volumetric efficiency is the name of the game.  The more combustible mix you can pack in, the greater the power yielded.

I can see it now in the Gunmaker's Hall at Friendship, a turbo-charged muzzleloader.

[mdtnhunter]

Good info....I had never thought about that.