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.

[crazyhorse1]

Note that elevation change will have more effect than temperature .

[max115]

@crazyhorse1.  Yes, good point, thanks.

[JPSAXNC]

@ crazyhorse1 What does elevation change?

[rsterne]

Cold air is generally more dense, and the speed of sound is lower.... A higher elevation is the reverse, and reduces the air density.... The higher the air density the quicker the slug slows down, effectively giving you a lower "local" BC.... Lowering the speed of sound means your shot is at a higher Mach Number, and the closer you get to Mach 1 (actually anything over about Mach 0.8 = 900 fps) the greater the drag, and again you will see a lowering in your "observed" BC....

High temperatures raise the speed of sound.... These effects are why you need to include your local conditions when calculating the ICAO (standard atmosphere) BC.... and conversely why your local BC must be corrected to take altitude, air pressure and temperature into account....

Bob

[avator]

I have a suspicion that the colder air temps affecting the pellet flight is not the only variable. Cold temps can also affect the functions of the gun. Seals are harder and lubes are thicker.

[Racing]

As much as i understand the thought behind presenting it as such, Mach is not a speed but a relative flight number.
Amongst other factors indeed affected by the common gas law.

[KevinJBrown]

The are so many variables, but most of them don’t have a great affect. Temperature is one that does for air rifles for lots of reasons not just during the flight. For this and other reasons, I recommend when shooting at longer ranges (consider anything over sixty to be long range for an air rifle) to keep a notebook of every shot.

[rsterne]

Mach is not a speed but a relative flight number.

Absolutely correct, and the Drag of a projectile is plotted against it, and all calculations are relative to it, not the "measured velocity".... The most important factor influencing the speed of sound (Mach 1) is the temperature....

Bob