What's the deal?

[4xforfun]

So, not wanting to hyjack another thread , I thought I would start another thread. I have seen the same question asked many times over the years:

"I am hand loading at 6000 feet( or whatever high altitude) and.......worried about PSI ". They list the altitude at which they are loading and or shooting when asking if a load is "safe".

Question......what does altitude have to do with hand loads (interior ballistics)? I certainly see the obvious connection with the bullet flight due to high altitude and EXTERIOR BALLISTICS....but for interior ballistics????

Do the Ballistic calculators have you factor in the altitude at which you are loading (or shooting) as far as powder charge when figuring PSI? Would not an over charge at sea level also be an overcharge at 10,000 feet.....or visa-versa?

Just stirring the pot,
Tod

 

[Mikemci]

Just thinking about it, I can't think of any affect altitude would have on the reloading process or interior ballistics. Will be checking back to see if anyone has other thougts to add.

 

[dkhunt14]

Just opinions from others, but I heard reports from loads too hot, from there loads here in the East. Also some reported there loads didn't shoot as well. This
is coming from a guy that moved to Arizona and a bunch of buddies that went to Colorado. I do know that the thinnner air makes them shoot way higher. Matt

 

[Alex Wheeler]

No change. My loads stayed the same from sea level to 5000 and I believe Tom won the 16 nats in Ga with the same load he shot in Mt.

 

[Mikemci]

The OP is asking about reloading and "interior" ballistics.

 

[4xforfun]

I'm talking about INTERIOR balistics.....what happens BEFORE the bullet leaves the muzzle.

Everyone and his brother knows that altitude changes EXTERIOR balistics.

Tod

 

[4xforfun]

No change. My loads stayed the same from sea level to 5000 and I believe Tom won the 16 nats in Ga with the same load he shot in Mt.

Right...accuracy shouldn't change....just WHERE on the target your group is located because of exterior balistics. Same goes with load development in the winter....keep you gun and ammo warm (hot) and everything that happens BEFORE the bullet leaves the muzzle will be the same as in the summer. Only thing that changes is where on the target your group goes.

Tod

 

[M-61]

Just a wag: There is less oxygen at 6,000ft than sea level. It's going to be a small amount (enough to cause a headache in some use to being at sea level. Maybe a shortness of breath). But the interior ballistics may be changed.

Would not an over charge at sea level also be an overcharge at 10,000 feet.....or visa-versa?

Another WAG: an overcharge AT 10,000 ft should be a bigger overcharge at sea level.

An internal (interior) combustion engine really starts to loose performance as the altitude increases. (Denver Heads----I'm dating myself!)
I guess one might say a rifle is a one stroke engine.

 

[Doug Beach]

Powder burn creates its own oxygen supply, unlike an IC engine.

 

[M-61]

Powder burn creates its own oxygen supply, unlike an IC engine.

Thanks...had no idea...

 

[mikecr]

Given the ratio of air density difference from ICAO SL pressure to std at 6000ft, you're looking at 2.4 PSI.
Now comparing that to the pressure behind a bullet, let's say 55Kpsi chamber to 6Kpsi muzzle, which would be 49Kpsi pressure drop over the barrel length, that's 2.4/49,000 or 0.005% relative.
If we were talking stoichiometric air-fuel ratio tuning, that would be one thing, but we're not.
We're talking pressure resistance change of 0.005% to a piston.
I don't see how it could make a difference.