FPS and Temperature change

[SteveKralsAround]

I'm curious as to the amount change .

If I set up an airgun for 880 fps at 40*F then in the spring arrives , the temperature goes up to say 80*F .

How much change in velocity would happen ?

 

[jtnm]

What I’ve noticed from my inside my apartment 64degs shooting over the chrono then going outside in 80deg temps over the chrono 10-15fps. Granted that the gun has been inside for a duration of time then able to stabilize to outside temp. 

 

[marquette]

Does the poi change from inside to outside with the FPS change?

 

[2fast2furious]

If you are talking about hpa. The difference is gonna be very small, the average shooter won't tell the difference. Hpa are not affected by temps as much as c02. C02 is more affected by temps, so it will shoot hotter during the summer vs the winter.

 

[8thman]

I can only speak for my lmpact mk2 25cal i loose about 10fps for every 10 degrees of cooler temperatures. I sight in my scope about an inch high @ 90 degrees at 50yrds and as temperatures drop so does my group and @ 40-50 degrees my poi drops to dead on. Find adjusting my scope, or in hot temperatures like 90 degrees plus I can adjust the power wheel. Hope that helps 

 

[L.Leon]

Back in September when I got my Bantam Sniper HR I shot some strings to get a baseline. Of late I noticed that when I took my gun outside into the cold (32-35 F) and immediately shot it my point of impact was at least one hash mark high. Then after a half hour or so outside it would settle back to its original POI. Before I noticed this I simply dialed my POI down, which I believe cost me three rats at 45 yards because I shot low once the gun got as cold as the outside temps. I decided to run three, ten shot strings to see if the numbers were much different than September’s. Shot outside in 32 degree weather all on level 6 of transfer port adjuster. I let the gun sit outside for an hour before chronographing. First up:

Crosman Premiers 14.3s / lo:919.6 /hi:925.2 / avg. 922.4 / es:5.62 / sd: 1.73. The average velocity was 24 FPS less than in September.

JSB Exact 18s / lo:860 / hi:866.8 / avg:863 / es:6.84 / sd: 2. The average velocity was 28 FPS less than in September.

AAs Diabolo Field 16s / lo: 895.3 / hi:908.3 / avg:900.7 / es:13 / sd: 4.58. The average velocity was 18 FPS less than in September.

 

[WHITEFANG]

Cold weather makes lubes thicker which will slow the gun down. How much I can not say because it depends on the gun and lubes used. 

PCP cold Rob's the air storage of psi. Hot weather increases the psi. Cold weather tends to change fps in both guns as with BP guns due to air density. Always allow the gun to acclamate for the best results. 

Hot to cold, cold to hot storage can result in condensation always. PCP fills can warm the tube or bottle. Expect psi drop as the container cools. JMO

 

[aa_limited]

lighting too will affect croney readings. so a bright summer day will yield higher fps than a dull fall day... even just due to lighting

 

[wahoowad]

I'm struggling with temp and fps now too, not sure if my difference is due to the weather or the gun.

Last week: avg. 965 fps @ 51 degree

Today: avg 917 fps @ 39 degrees

Looks like way too much drop for a regulated PCP to just be the weather. Really friggin annoying

 

[wahoowad]

So I just went back to my garage and decided to change the 9v battery in my Alpha Chrony even though the other one seemed to be working fine. My shot string went from avg 917 to avg 936 fps. This is maddening for me because it can be so hard to tell if I'm experiencing a chrony issue (I use their light kit) or a gun issue.

If I accept my new numbers of 936 fps, and attribute the difference to the new battery, then I am roughly 25 fps lower today at 39 degrees than 965 fps a week ago at 51 degrees. Still a larger drop than I expect.

I have no way to verify the chrony so am always suspicious of it's output, especially when I see variability between shooting sessions. One time I spoke to the Shooting Chrony tech support and they said I could send it back to check the calibration, which made me then always wonder if the calibration was off and how I would even know. I did shoot my chrony by accident one time but it still seems to function so I assume it is working.

 

[lenweber2]

Factor in the lower temps making the lead harder so less seal to the barrel in colder weather. Then again it could be do to that ever present Chandler wobble that seems to afect most everything we do. Gin lube in the cold weather seems to help but accuracy goes away.

 

[ctshooter]

I can't speak for the fps as I didn't have a chrono and the gun is regulated so it may not have played into the shot. But, I took my Leshiy and guppy tank from 70* indoors to a friends house where we shot outdoors in 35-38* temps. I noticed that when I pulled them out of the bag both the gun and the guppy tank had lost 500psi from when I left the house. 

 

[Nteesupreme1]

I have the umarex notos my rifle Will shoot 730 FPS at 60°F 720 FPS at 70°F 710 at 80°F and 700 FPS at 90°F. And I can't explain it only thing I can think is the higher temperatures increase the pressure in the regulator and slow down the projectile some way like the regulated creep does

 

[Airgun Al]

I have the umarex notos my rifle Will shoot 730 FPS at 60°F 720 FPS at 70°F 710 at 80°F and 700 FPS at 90°F. And I can't explain it only thing I can think is the higher temperatures increase the pressure in the regulator and slow down the projectile some way like the regulated creep does

That is interesting.
I would have expected the exact opposite.

 

[Nteesupreme1]

Yes I was shocked this is my 1st regulated gun. I noticed that when the gun has sat for more than 24hrs the 1st shot is 15fps or more low. I was told that it was regulated creep where too much pressure has built up

 

[Stubbers]

Yes I was shocked this is my 1st regulated gun. I noticed that when the gun has sat for more than 24hrs the 1st shot is 15fps or more low. I was told that it was regulated creep where too much pressure has built up

Yea this is one caveat to most regulated and even guns that boast balanced valves (for a different reason). The hotter you tune em (closer to the plateau for a given pressure) the better they are at circumventing a low fps cold shot.

-Matt

 

[JimD]

I agree with Matt. My 3 P35s (made by SPA like the Notos) will all give me a low velocity first shot when the hammer spring is adjusted to give me 5% less velocity than the peak for that regulator setting. The amount varies a bit gun to gun. Turning the hammer spring back up a little will make it closer or even make the low velocity go away. I thought my Caiman X with a Huma regulator was a little better but I just checked it and I do not think it is. It was at least 13 fps low on the first shot with the average velocity about 5% below the peak. For that gun it means the first shot is about 1/4 inch lower at 30 yards. For many purposes this is trivial. But for 30 yard challenge targets it is significant. I guess I need to just waste the first shot. I want to shoot a few targets at it's current ~890 fps velocity but I may turn it up further. If I do, I will try to remember to check the first shot velocity.

 

[Rizz01]

In my personal experiences, guns with large plenums can be affected more so by temp change. I actually take the gun I'm shooting and sit it outside for an hour or so before a session. It's about 66 deg F in my house and the weather here where I live has been mid 90's to 100 lately. Total waste of time for me to shoot unless the gun warms up.

 

[Ta-Ta Toothie]

I definitely agree with the large plenums. Living in the desert mountains, you need to adjust with the big temperature swings. Couple clicks here and there.

 

[Rizz01]

I had a habit of resting my thumb on the top of the plenum on one of my guns. POI would go off the rails. I shoot for long periods of time. My ole' lady would call on me to eat so when I got back, POI would drop back to my original zero but creep again after 15 minutes or so. I thought there was a reg or seal problem so I looked it over and didn't find anything wrong. After a few days passed, I happened to read an article regarding things that may adversely affect POI. Making contact with the plenum was listed. Next day I happened to notice my bad habit. Haven't had that issue since.
Lesson learned....