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Air Gun Home Forum Index » General Air Gun Questions and Topics » Altitude & pellets Goto page 1, 2  Next    View previous topic :: View next topic  Altitude & pellets   Posted: Sun Nov 14, 2010 7:42 am 720fly Veteran Member Joined: 17 Oct 2010 Posts: 150 Location: a top of the Mountain of dreams A Question about thin air and effects on a pellet in flight. Up here at the Leadville golf course, anybody can gain 20 yards on their drive because of the thin air So do you think I am getting more fps? would this allow pellets to fly differently due to temps. at above 10,000 ft just a thought that became a question   Posted: Sun Nov 14, 2010 8:43 am jlwilliams Veteran Member Joined: 02 Oct 2009 Posts: 264 Location: Jacksonville, NC USA A thought that became an excellent question. You, my friend, need a Chronograph. Watching to see what I can learn from this discussion......   Posted: Sun Nov 14, 2010 10:58 am fritz Silver Status Member Joined: 25 Nov 2008 Posts: 2444 Location: New Jersey- outside of Philadelphia More fps? Probably not. In a pcp the pressure should be greater for the same volume coming up from sea-level. The puff used to shoot would also face less resistance from the atmosphere. In a springer, the thinner air will compress to a lower pressure during the piston stroke, giving it less power. Either way, your pellet will have a higher BC because the thinner air provides less resistance upon it. You may not be shooting faster, but if you calibrated the gun to shoot Xfps at sea-level, and then tuned it at altitude to shoot Xfps again, your pellet will fly further due to the higher BC. _________________ "I never set out to be wierd, it was always everyone else who called me it" -Frank Zappa Speed is impressive, accuracy is deadly. It's not that I'm not a people person, it's just that I'm not a stupid people person.   Posted: Sun Nov 14, 2010 11:08 am 720fly Veteran Member Joined: 17 Oct 2010 Posts: 150 Location: a top of the Mountain of dreams Well I'm shooting the Benji np xl 1100 .22 , I took it down to denver to shoot some stuff for friend, and it was shooting pretty low(3 inches) so I adjusted it. Then when I got home it was hitting 3 high, so I figured there must be some thing to it   Posted: Sun Nov 14, 2010 1:07 pm fritz Silver Status Member Joined: 25 Nov 2008 Posts: 2444 Location: New Jersey- outside of Philadelphia Didn't think the difference would be that great. _________________ "I never set out to be wierd, it was always everyone else who called me it" -Frank Zappa Speed is impressive, accuracy is deadly. It's not that I'm not a people person, it's just that I'm not a stupid people person.   Posted: Sun Nov 14, 2010 3:28 pm Slavia Moderator Joined: 31 Mar 2008 Posts: 4382 Location: Waseca, Minnesota, USA Quote: Well I'm shooting the Benji np xl 1100 .22 , I took it down to denver to shoot some stuff for friend, and it was shooting pretty low(3 inches) so I adjusted it. Then when I got home it was hitting 3 high, so I figured there must be some thing to it At what range? _________________ ¡Listo! ¡Apunte! ¡Fuego!   Posted: Sun Nov 14, 2010 4:08 pm 720fly Veteran Member Joined: 17 Oct 2010 Posts: 150 Location: a top of the Mountain of dreams 100 foot, the 3 inches were the largest of the spreads. Plus that just eye ballin it   Posted: Sun Nov 14, 2010 7:36 pm Slavia Moderator Joined: 31 Mar 2008 Posts: 4382 Location: Waseca, Minnesota, USA An interesting observation worthy of more study. Google tells me that when I'm centered on the capitol building in Denver, the elevation is 5240' A.M.S.L. (truly making it the "Mile High City"). The Chamber of Commerce in Leadville is at 10,213. That's quite a difference. _________________ ¡Listo! ¡Apunte! ¡Fuego!   Posted: Sun Nov 14, 2010 8:53 pm sniper Silver Status Member Joined: 28 Nov 2008 Posts: 3752 Location: Star, Idaho This thread has my attention.. Bob? _________________ I believe in gun control, If there's a gun around I want to be controlling it.......   Posted: Sun Nov 14, 2010 9:49 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC It's a springer, so my guess is that the amount of air (ie the weight or mass) inside the chamber is significantly less at high altitude.... Since the weight of the pellet is the same, just based on momentum transfer, I would think that the pellet will receive less energy and hence have less muzzle velocity.... A chrony is needed to confirm.... In a PCP since the pressure in the reservoir is hardly affected by the reduced atmospheric pressure (the gauge pressure would be immeasurably different).... I would think the muzzle velocity would be nearly the same.... The pellet should in fact hit higher because of the reduced air resistance.... With CO2, as long as the temperature is the same, I would expect similar results to a PCP.... With a pneumatic, I would expect results in between.... It would take more (but easier) pumps to cram the same amount of air into the valve.... If you pumped to a given pressure, then the gun would shoot like a PCP.... If you pumped a set number of pumps, it should behave more like a springer.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Mon Nov 15, 2010 1:24 am Slavia Moderator Joined: 31 Mar 2008 Posts: 4382 Location: Waseca, Minnesota, USA Quote: my guess is that the amount of air (ie the weight or mass) inside the chamber is significantly less at high altitude http://www.engineeringtoolbox.com/air-altitude-density-volume-d_195.html It looks like the density of air at 10,000' is about 17% less than at 5,000' (and since the swept volume of the springer is the same, density translates to mass). Anybody know of a ballistics calculator that will show the effects of altitude? _________________ ¡Listo! ¡Apunte! ¡Fuego!   Posted: Mon Nov 15, 2010 9:25 am 720fly Veteran Member Joined: 17 Oct 2010 Posts: 150 Location: a top of the Mountain of dreams Just so you know the Benji has the Nitro piston, not a spring Another question, I have the opportunity to trade my gun for a disco, I am a survivalist. that being said the thought of pcp scares me, but the accuracy is beyond the break barrel, with longer range What to do? I really can't see a hand pump that can break, as a viable tool. If I do this trade I'm looking at many $$ mods and still have a non-self contained air riffle This is way to hard to decide, so some help would be nice And is shroud,muzzle break another way of saying silencer? cause the disco is loud   Posted: Mon Nov 15, 2010 11:54 am rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC Using Chairgun3.... go to the Configure menu and click on "Environment".... At a range of 100' for 750 fps & BC=0.033, the POI is about 0.1" higher at 10,000 ft altitude than at sea level.... Incidently, if the velocity loss was proportional to the difference in the mass of air in the chamber (17%) that would reduce it (in the above example) from 750 fps to 622.... and would cause the pellet to hit about 1.4" lower at 100'.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Mon Nov 15, 2010 4:21 pm LittleRickie Member Joined: 01 Nov 2010 Posts: 73 Location: Fairport New York and ADKForun.net 720fly wrote: Just so you know the Benji has the Nitro piston, not a spring No thin outside air is being pumped in. In thin air I would think it would go farther. I guess.   Posted: Mon Nov 15, 2010 5:47 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC Quote: No thin outside air is being pumped in I don't think you understand how a Nitro Piston works.... It simply takes the place of the spring.... It works exactly the same as any other springer.... except the spring is a cylinder of nitrogen under pressure.... just like the gas spring on a car tailgate.... It still drives a seal down the chamber at high speed to compress air and fire the pellet.... That air enters the chamber through the transfer port in the breech.... so if you are at a higher altitude fewer molecules of air enter the chamber to be compressed.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count! 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