Cold temperature affecting projectile's flight

[Max115]

The cold temperature has affected my POI with reduced speed of my slugs. A reduction of 15-20 fps has changed my accuracy and all my shots were lower. so I had to re-zero all my aim point to match the lower speed and luckily I only had to make a minor adjustment to the valve by opening it up 1/8th of a turn.

My Impact was shooting the 25gr slugs at 984fps with great accuracy before. Now my speed has dropped to 967fps. I didn't want to mess around with the Reg or HS. Only a small turn of the valve adjustment was all I needed to get good accuracy back. I will continue to monitor the speed of the slugs to see if I need to make further adjustment.

Enjoy.

 

[jetpopt]

Cold air is denser than warm air.

 

[Motorhead]

Cold air is denser than warm air.

EXACTLY .... Lowering the projectiles BC value while in flight to target.

 

[Motorhead]

What I found was the same as the OP, in could weather the muzzle velocity is lower than in warm times.

Same issue as Sea Level verses Higher Altitudes

 

[thomasair]

It's not quite the same issue. It's two separate issues. Internal and external. The internal problem is that air guns shoot slower when cold and faster when hot. The lower poi problem in the cold is exacerbated by the thickness of the air after leaving the barrel.

Both can be solved simultaneously by a mechanism in the gun that increases velocity as the ambient temperature goes down....such as the mechanism in the Thomas FT.

Mike

 

[Motorhead]

I did not know that at the same temperature the ambient pressure will influence the pressure inside the reservoir and spring energy.

In a PCP, pressure within containment will not shift with barometric pressure fluctuation, But does with temperature shifts.

It is the resistance the ambient air has upon a projectile passing threw it that shift the velocity Cold / Hot or Low / High elevation.
Simply an air density thing

 

[Motorhead]

You've lost me ?? One effects the other

 

[Motorhead]

Muzzle velocity effects poi but poi does not effect muzzle velocity.
The OP talked about muzzle velocity and I confirmed it.

Stated ONE effects the other .. NOT both

 

[RickH]

Looks like 2 problems. The gun and air tank get colder, pressure drops so muzzle velocity would likely be affected. Cold air is more dense. That’s why airplanes climb better in colder air. Denser air would likely cause at least a little loss of velocity at the muzzle.

Rick H.

 

[airprsr]

Cold weather like we’re having right now plays havoc with my carefully tuned guns, lowering the speed and changing the harmonics of the tune, causing me to have to come up with new holdover tables. And top it all off with how rapidly the weather can change. I plan to shoot an upcoming nrl22 match and I’m feeling like I have to do my preparations on a day when the temperatures are same as they will be on match day.

 

[Max115]

@Klaas. Thank you for your write up. Very interesting to learn about the science part. Cold temperature definitely affects the performance of air guns, tuned or not tuned properly. The process of finding the "harmonic tune" is long and tedious. I believe I have found my tune with the Reg/HS combination of my Impact shooting the H&N 25gr slugs. I haven't make any adjustment to the Regulator or HS since. I just adjust my POA to allow higher aim for each distance. I am curious to see if my POA/POI returns to normal in the Spring/Summer.

 

[DesertSilver]

Another thing that cold Temps can do is thicken the lube on the hammer causing it to not strike the poppet valve as hard.

 

[Max115]

@Klaas. All good. Learning new things everyday. cheers.