effect of cold on accuracy

[whitetaildreamer]

In all the decades of hunting here's something I've never really concidered. When I sight in my rifle it is usuallyduring the summer butrifle deer season is not untill the end of Nov. to the end of 1st week in Dec. I've never had a difficulty putting one in the boiler maker at 300 yards with the ol'7mm mag so I've ner really considered it. Has any one experimented with this? Maybe with it still being -15 to 20 up here I might go out a punch some paper just to see if there is any real difference to when it gets warm.

[Pawildman]

Loads that are developed in the warmer weather and found to deliver optimum accuracy at or near max powder charges often do not give the same degree of accuracy during colder weather, and vice/versa. Example: I worked up a load for my 7-08 in August. 47 gr. of IMR 4350 gave good, consistent groups. 48 gr. was spreading out. In Nov., I checked it again, as I felt the cooler weather would probably affect it. It did. The 48 gr. loading was now the most accurate for that gun. What really becomes a problem is if a load is developed in the cold season at max or near max powder charge, and then tried in the heat of summer. Pressures can rise to the point of sticky bolt lift or worse, and/or case heads taking on bolt face features. Near max, max, and over max charges should be approached cautiously. Accuracy will usually be affected also.

[whitetaildreamer]

I've been loading my own for this particular 7 mm mag for about 20 years. I too am using 4350 powder. The load that this particular rifle likes (has produced the greatest accuracy) is about 8% off the max. suggested load (shooting during the summer months...100's of rounds per season. Thank god for the recoil pad). Why I asked this question is the deer I took this last season (approx. 175 yards give or take a couple) the shot sound seemed to be of a higher pitch and the hit on the deer up and to the right about 4 inches. Well within the kill zone but the day that I harvested the animal it was -35. Perhaps the sound difference was due to the cold or the difference of atmospheric pressure associated with the day. I think if I would have pulled the shot it would have been to the left. So thus the reason for the question.

[kdvollmer]

General rule of thumb for shooting. Not an exact science, but it is what is taught to military snipers.


From any given temperature the following will happen:

for every 20 degree increase in temp from your zero, you can expect a 1 MOA higher POI ( point of impact )
for every 20 degree decrease in temp, your zero will be 1 MOA lower


For given humidity:

For every 20 % increase in Humidity, round will strike 1 MOA low
For every 20 % decrease in humidity, round will strike 1 MOA higher.


And yes, they can work against each other. If you have a 20 degree increase in temperature, and a 20% increase in humidity, then there SHOULD BE no change.


Hope that this helps some. Good Luck.

[HEAD0001]

Well put KD. I hope you are always on my side.

IMO temperature and humidity have less to do with accuracy, and more to do with POI. Just like elevation. Tom.

[stubblejumper]

A change in temperature can effect the chamber presure produced,and therefore the velocity.In effect it is like changing the powder charge,so the point of impact can also change.From my experience,the loads whose accuracy seemed most sensitive to adding or subtracting a grain or two of powder were most effected by a change in temperature.If the accuracy was very consistent when a grain or two of powder was added or subtracted,the accuracy was usually quite consistant with changes in temperature.

[whitetaildreamer]

Thanks for the info guys.