The weather component you probably should start taking into account

Thanks! Now I have yet another excuse for why I sometimes miss! LOL!

Seriously, I did not realize the changes in POI could be that high for temperature!

It does explain some of what I have experienced.

There is 1-1.5 MOAs of difference between my winter zero and summertime zero at 40 yards depending on whether I'm shooting JSB Exact Jumbo 18s or Crosman Premier 14s.

Thank you for sharing your weather tracking results with us. I have noticed that the change in ambient temperature going from inside to outside changes the actual gun characteristics quite a bit due to expansion and contraction of the metals as well as the air pressure within the cylinder.

Environmental conditions to include temperature, humidity, barometric pressure,etc. Have always had an effect on external ballistics, from pellets to 120mm tank cannons and up.

Temperature has always been the biggest factor. the others play, but compete with the shooter, which tends to be a larger factor in most cases.

Air is the propellant, and like propellant will act on the projectile differently when it is cold vs hot.

Then add Barrel temp, BP, Humidity.

Back in the day, when we would boresight the guns on our tanks, prior to gunnery, we would recheck our boresight if there was a 10 degree or greater change in temperature.

The ballistic computers would factor in all the Enviromental's as well. Even ammo temp.

Look at any ballistic calculator and how slight changes will affect POI (Point of impact)

Those are interesting statistics. I'm not as scientific as you, but I do know that if I start shooting in the shade, and an hour later the Sun is shining down on my rig, the POI is going to shift.

Hmmmm, this got me thinking. 

Does the projectile velocity drop significantly shooting in colder weather, causing POI shifts? Maybe that’s what is being inferred here as it relates to extreme temp changes. I.e., big velocity swings?

I recall shooting my first and only 2020 virtual Extreme Benchrest target in really cold weather, and believe my velocity had dropped unbeknownst to me at the time. I remember being surprised at how low my shots were hitting at 100 yards, and always wondered if the cold temperature lowered the velocity. 

Just to clarify. I'm shooting from a heated indoor location out my back sliding glass door to a target 50 yards away outside. That means the gun is actually pretty close to room temperature whether I'm shooting in the hot summer heat or during freezing winter temps. The POI drop seems to be directly caused by the pellet slowing down in the cold air. However, I notice the same phenomenon at the range. If I sight in on a cool morning and then go back out shooting after it has warmed significantly during midday, the POI shift I describe will occur. The velocity from the gun is consistent (I rarely shoot without my chronograph).

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@mmahoney This is actually pretty interesting. What I’m curious about is this, when you noted the POI drops, were you shooting from a fixed rest? Like the type some people use when they zero scopes? I’m specifically referring to when shooting outdoors, but if you did while shooting from indoors I’m interested in your response to that question as well. I’m trying to wrap my head around this as it’s relatively new to me. 

Laws of physics would dictate that air density increases with drop in temperature, among other things, too:

https://en.wikipedia.org/wiki/Density_of_air

I shoot from a heated room during frigid winter months in Minnesota. Its very common for me to experience POI shifts based on relative humidity and temperatures. Air guns are much more finicky than firearms. That's my observation, fwiw.

“The POI drop seems to be directly caused by the pellet slowing down in the cold air.”

So, the velocity DOES drop in cold air. This is my understanding from the last few posts and has been my experience as well.

Thanks for doing the research!

Tom 

Air is about 93 percent as dense at 86° f as it is at 50° f. So it should be about 7% easier for a pellet to travel through the air at 86°, then it is at 50°. Seems to me that in the case of a spring air rifle for example the rifle would be more efficient by something like 7% at 50°, then 86°, but I don't believe that's what experience shows or maybe it does. Just thinking out loud I believe I should have a look at my copy of the air gun from trigger to Target

Cold air is thicker than warm air. There is a 1.4 inch difference on my 95y target from 20 degrees and 110 degrees 

And that's what Chairgun says it should be 

I to am shooting from a climate controlled room 

mmahoney did your poi move only up or down with temperature changes or did you also experience left or right poi changes (excluding the wind)?

Gary

Its around -30 to -40 here today.... would love to add some data points to your list, but I also don't want to freeze my "pellets" off

@Ezana4CE

I'm shooting from a Caldwell Stinger rest on top of a table I have modified to remove any wobbles from it. My scope is a March 10-60x56 HM scope. My gun is a .22 cal Taipan Veteran Long. The gun and rest are predicable and consistent enough to shoot perfect scores on National50 benchrest practice cards.

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Thanks that’s what I was wondering. The variables mentioned helps me to work on my longer shots. 

@Ezana4CE

I'm shooting from a Caldwell Stinger rest on top of a table I have modified to remove any wobbles from it. My scope is a March 10-60x56 HM scope. My gun is a .22 cal Taipan Veteran Long. The gun and rest are predicable and consistent enough to shoot perfect scores on National50 benchrest practice cards.

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I have a .25 Vet Long and can’t shoot higher than a 235 average for N50. Would not mind seeing some of those ‘perfect 250 scores’ with your Vet. 

I have to agree with your temp findings, but cant agree about humidity...my many years of airgunning has shown that high humidity also affects poi.. When humidity is high the velocity drops on my chrono which causes a shift in poi. Have made numerous tests over a chrono under various levels of humidity and found high levels have always shown lower velocities at least it has in my airguns.