PCP at High Altitude -- Bursted Airtube? -- Shooting Performance?

[JungleShooter]

We just had a question here on altitude and high temperatures.
Here's a similar one, but different (yeah, I'll make sense in a moment).

So, what about PCPs at high altitude: 11.500 (3.500m)?   
I'll be taking a trip, and I'd love to take a PCP along, but... is something going to burst?   
Do I have to lower the pressure to say 200bar before heading up the mountain?
What about air tanks, like a SCBA?
What about my shooting performance -- how is high altitude going to affect performance?

It's a Skyhawk (P-15), with a 250bar air tube.

Thanks for the help!

Matthias

[Nvreloader]

JS

I take my SCBA air tanks/PCP rifles, 2500/3000psi fill, up to 5500/7000' levels on deer hunting trips,
and have never had a problem, I always check the zero's at camp after a bumpy ride to camp etc.   

HTH's,

Don

[Techie]

Trajectory gets flatter at higher altitudes, especially as high as you are talking about.   However you won't notice the difference at airgun ranges.  It matters quite a bit when shooting 500 yards at 11,000 feet, like when I'm hunting elk.  I think many elk have been missed at high elevation by shooting over their backs as flatland hunters think their bullets are going to drop more than they do.

The nice thing about PCPs is they don't lose velocity at higher altitudes like springers and pumpers.  I won't even shoot a springer at 11,500 feet elevation.  I'm afraid of the piston seal slamming into the front of the cylinder.  No worries with a PCP.

[rsterne]

There is NO danger of bursting a tank due to altitude.... Even at the top of Mt. Everest you would at most add only 10 psi to the pressure differential inside and outside the tank....

Temperature is also not a danger, provided you are not overfilling the tank or gun.... The pressure increase due to a rise in temperature is proportional to the ABSOLUTE temperature.... 20*C is 293*K, and 40*C is 313 *K.... For that 20*C increase in temperature, the pressure would increase by (313 / 293) or about 7%.... That would be roughly 200 psi on a 3000 psi fill.... nothing to be alarmed about when you consider that a 3000 psi tank is tested to 5000 psi, and has a burst pressure of about 10000 psi....

In a regulated gun you will notice NO difference in performance.... In an unregulated PCP, properly tuned to a bell-curve, you may notice a decrease in velocity for the first few shots until the pressure drops back to 3000 psi.... In cold weather (eg. 0*C) if you filled your tank to 3000 psi at 20*C and then cooled it, the pressure  would drop to (273 / 293) x 3000 = 2800 psi, so your first shots might be a few fps faster and you would get fewer shots before the pressure dropped to your refill pressure.... In a regulated PCP, you would notice only a few less shots, but as the regulator setpoint doesn't change, neither would the velocity....

Bob

[Stinger177]

There is NO danger of bursting a tank due to altitude.... Even at the top of Mt. Everest you would at most add only 10 psi to the pressure differential inside and outside the tank....

Yep!

You could take a tank from sea level to outer space and the internal pressure would increase 14.7 psi. 

[JungleShooter]

Thank you all for taking away my worries! 

I had read a post on some forum that included a stern warning about PCPs & tanks at high altitudes.... 

That's when I knew I had to ask my specialist friends on THIS forum. The issue is just too dangerous to take just anyone's word for it.

Matthias   

[billzweig]

The air pressure at 3500m is about 0.65 bar, or about 5psi lower than sea level. Even in space the pressure is only 15psi lower so no danger to the air tank. But the range of a pellet in space would be infinite.... 

[wimpanzee]

You're likely to see a lot more compressed pressure change from temperature changes at altitude than ambient pressure change.

[HunterWhite]

I would expect the Balistics to be better since the air is thinner. The pellet will not slow down as quickly at higher altitude. If you want to shoot 100 yards then you may need to check the point of impact when you get there. Maybe Chairgun or Streloc can tell you more.

A 25 grain pellet with a bc of 0,1 leaving the muzzle at 900 FPS, 45 FPE will drop 9,4 inches at 100 yards, giving 34 FPE at 784 FPS.

The same pellet at 11500 feet leaves the muzzle at 900 FPS, 45 FPE will arrive at the target going 819 FPS for 37 FPE, with a drop of 8,6 inches.

I would also expect the pellet to leave the muzzle faster than 900 FPS since the air in front of the pellet is less mass.

[JungleShooter]

THANKS for your replies, very helpful. 😊
Didn't think of some of those factors you mention. Good thinking.

Well, my trip to the roofs of South America was canceled — transmission makes a sound like a pig just before it gets turned into pork....

But I still want to go on a mountain trip, so this info is helpful nevertheless.

Thumbs up! 👍🏼

Matthias