Range Report Temperature?

[PMR14]

Hi SH,

Last week at the range, I noticed that my 1000yd shots were falling short than previously in the warmer weather. 700 yds was on target, but I needed raise my elevation about 25" than i have in the past for the 1k shots. The temperature difference was about 50 degrees (75 in the summer and 25 at the range). Has anyone seen similiar drops, especially at longer distances? Is temperature affecting this difference? I was unable to chronograpgh my shots, but shots from 200-700 were on target. No shots taken at 8-9 hundred.

Thanks,

RG

7mm mag
162 Amax
4831sc 62gr
Norma brass
Fed 215m

 

[7mmShooter]

the temperature is having an effect on your shots yes, but generally the colder the air, the less dense it is. which would make the bullet fly with a bit less drop because of the decreased air density. hopefully someone who has experience with this will chime in.

 

[Bob 964]

the temperature is having an effect on your shots yes, but generally the colder the air, the less dense it is. which would make the bullet fly with a bit less drop because of the decreased air density. hopefully someone who has experience with this will chime in.

[FONT=&amp]Isn't cold air more dense than warm air? As air temperature decreases, the air becomes more dense and your bullet will fly less efficiently and with a lower velocity. If you zero your weapon at 75˚F and fire it at 25˚F,the increased air density will cause the bullet to fly slower and have a lower POI on your target. If temperature goes up, POI goes up; if temperature goes down, POI goes down. [/FONT]

 

[oathkeeper]

^ that color didn't show up too well on my screen but you are right. Cold air is more dense than warm air. Your POI will lower in cold weather. If your powder is temperature sensitive that will have a large shift also.

-Dick-

 

[40xs]

It has more to do with the burn rate charactoristics of the powder than air density. It has always been a factor in the velocity difference between warm temps. and cold. Some powders do better than others, but generally, all powders are affected by temperatures. Ie; the reason that a close to max. load will become overmax on hot days, or, if you cook your round in a hot chamber prior to sending it. Your impact on a 1000 yd target can be several inches higher if you leave a bullet in a hot chamber too long. My loads using RE17 in the winter will print close to 40'' lower than summer zero at 1000yds.

 

[George63]

lots of bad internet conjecture going on here - run both temps on this:

JBM - Calculations

as this thread, in only a few posts has shown - forum replies are unreliable and often wrong

 

[7mmShooter]

ah i see now that i am wrong. I mix these up quite a bit, so im sorry, but is good that people have chimed in to clear things up.

 

[PMR14]

40xs: what caliber are you shooting? Looks like my gun shot 25-27" low at a thousand, but the interesting thing was that it was dead on at 700. Maybe the longer distance played a big enough of a role to make the diffference.

George63: I ran the calculations on the calculator, the computer says about 1 MOA less with the colder temp.

So I ran the specifics through the computer app i have been using, seems like a 100 ft/sec MV slower would equal the same drop at 1k. BUT, all my dope was off. Weird.

 

[colson]

Air density and muzzle velocity greatly influence time of flight and thus the required elevation setting on your sight.

Ambient air temperature has a major effect on air density. Ammunition temperature can have a great effect on muzzle velocity. This is powder dependent, or so I have read. I'm trying to nail this down for my chosen ammunition.

I'm a fan of carrying my ammunition so that it is near to ambient air temperature. This removes one variable so long as I take care to fire the chambered round (in a hot gun) quickly.

 

[George63]

40xs: what caliber are you shooting? Looks like my gun shot 25-27" low at a thousand, but the interesting thing was that it was dead on at 700. Maybe the longer distance played a big enough of a role to make the diffference.

George63: I ran the calculations on the calculator, the computer says about 1 MOA less with the colder temp.

So I ran the specifics through the computer app i have been using, seems like a 100 ft/sec MV slower would equal the same drop at 1k. BUT, all my dope was off. Weird.

so you are saying, according to the ballistic programs the air density ( colder temp ) accounts for 10 inches of the 25 inch change - with H 4831 the MV should not account for all of the rest, so you must have another variable that is not completely nailed down

 

[colson]

I read an article that described a test on temperature effect on POI. The test rifles were cooled and heated while the ammunition temperature remained the same. The rifles exhibited POI shift from zero due to the temperature change.

Long Range Shooter| Temperature Effects on Zero

 

[PMR14]

Hi George,

So the temperature difference does affect my drop 1.2 MOA. I am guessing that since I loaded my last rounds at the range ( the rounds I shot at longer distances) with my pocket scale, the scale could have been off. I re-ran the number with 30ft/sec less and it makes up the difference.

So temp does affect the point of impact and any other variable may greatly influence the difference.

Thanks George for your help and input.

RG

Thanks for all the responses!

 

[40xs]

PMR14, I shoot a .308, primarily 185 Berg., however my biggest change in impact was with the 208 Horn. and RE17. Zeroed in the summer but shooting a match in the winter I had to come up right at 4 moa. Just not enough case capacity to satisfy what i was looking for so i went back to the 185-190 bergs. and Varget.

 

[oathkeeper]

Chrono your bullets and make your own drop tables.

-Dick-