Pressure Signs when Changing Elevation, Questions?

[Killer Deal]

Hey all,

To date, most all of my shooting as been at sea level to about 1,000' elevation. I'm getting ready to work up some load development for the Nightforce ELR match in Wyoming. I've done some searching and couldn't find a clear answer. (DAs up to 2500 on a hot humid summer day for my local New England east coast shooting)

Do I need to worry about developing pressure signs load developing at sea level and then shooting at 5,000' in the summer time? or would the problem arise the other way around? (expecting DA to be around 7,000 or higher in June in Wyoming)

Context: I generally settle up loads close to max or slightly over max charges (published) for competition shooting.

 

[_Windrider_]

Hey all,

To date, most all of my shooting as been at sea level to about 1,000' elevation. I'm getting ready to work up some load development for the Nightforce ELR match in Wyoming. I've done some searching and couldn't find a clear answer. (DAs up to 2500 on a hot humid summer day for my local New England east coast shooting)

Do I need to worry about developing pressure signs load developing at sea level and then shooting at 5,000' in the summer time? or would the problem arise the other way around? (expecting DA to be around 7,000 or higher in June in Wyoming)

Context: I generally settle up loads close to max or slightly over max charges (published) for competition shooting.

The DA change isn’t what will cause pressure it’s the temp. If you load super hot at 70 degrees just below where you see pressure signs and then go to Wyoming where it’s 90 you could see those pressure signs. If using factory ammo I wouldn’t sweat it.

 

[RegionRat]

Agree. Watch your temperature margin for driving the muzzle velocity and cartridge pressure issues.
Watch your climate for overall DOPE.

Internal ballistics are driven by the cartridge load recipe and those can be affected by the temperature of the day.
External ballistics are affected by the climate and will drive your DOPE, but to the first order the internal ballistics are driven by the charges and temperature.
The amount velocity change based on climate change of the air compressed in the bbl as the bullet travels is negligible in terms of cartridge pressure and muzzle velocity, but all the air between the muzzle and the target matters to your DOPE.
You can select powders that are more or less temp sensitive, and you can select the powder charge for the tune and how much margin it has to pressure. You don't get to select the weather of the day you have to shoot, so it is a good idea to understand how much margin you have on your tune, not just on the hot side but also on the cold side. YMMV.

 

[Rocketvapor]

Internal Ballistics:
You could probably kick UP the load with a 7000 DA.
At least by 5 PSI
A 0.1 degree F change in cartridge temperature is a little more than that.

 

[Killer Deal]

The DA change isn’t what will cause pressure it’s the temp. If you load super hot at 70 degrees just below where you see pressure signs and then go to Wyoming where it’s 90 you could see those pressure signs. If using factory ammo I wouldn’t sweat it.

Gotcha that makes sense, I will be reloading. I'll have to do number crunching on the temp sensitivity.

 

[Killer Deal]

Agree. Watch your temperature margin for driving the muzzle velocity and cartridge pressure issues.
Watch your climate for overall DOPE.

Internal ballistics are driven by the cartridge load recipe and those can be affected by the temperature of the day.
External ballistics are affected by the climate and will drive your DOPE, but to the first order the internal ballistics are driven by the charges and temperature.
The amount velocity change based on climate change of the air compressed in the bbl as the bullet travels is negligible in terms of cartridge pressure and muzzle velocity, but all the air between the muzzle and the target matters to your DOPE.
You can select powders that are more or less temp sensitive, and you can select the powder charge for the tune and how much margin it has to pressure. You don't get to select the weather of the day you have to shoot, so it is a good idea to understand how much margin you have on your tune, not just on the hot side but also on the cold side. YMMV.

Sweet, that makes sense. And good point on the temp sensitivity. I'll have to do some number crunching for the 300 PRC I'm reloading for. I'll be trying 7828scc and ramshot LRT for the match so I'll have to work that out and maybe wait till spring to work out the load development so I have time to confirm preliminary dope before the match.

Thanks for the help.

 

[Killer Deal]

Internal Ballistics:
You could probably kick UP the load with a 7000 DA.
At least by 5 PSI
A 0.1 degree F change in cartridge temperature is a little more than that.

I'm ordering some PVA 212gr seneca copper solids for the match and with a DA of 7k at 75° its supersonic to 2,400 yards at 2,900 fps. Not that 2,000 yards at 2900fps, supersonic with 225gr ELDms is anything to scoff at either under those conditions.