Change in point of aim - causes

[C.W. Richter]

I do not believe temp/humidity is your issue, especially at hunting distances of 300 yards or closer.

Bullets will sail a bit in warmer weather, but you really don't start seeing much effect until you get out to say 500 yards.

I just ran a test through a ballistic calculator
160 gr bullet at 2900 fps with BC of .45, 100 yard zero, 90ºF = 49.4" of holdover at 500 yards
same variables as before, except tempt at 40ºF = 51.5" holdover

The effect will be greater in low BC bullets, and less in high BC bullets. But the change is still quite small, even considering different BCs

Yes. Any issues i ever had were 200 yds+ and I suspect sub-zero temps may have additional effects on the metal(s), and/or even bullet selection, especially on that crucial, first shot! I've narrowed it down to specific guns, and simply don't opt to use them under such conditions. Other combos appear to "weather" the situation better.

 

[sgt_zim]

at 90º F

at -10ºF

still no appreciable difference until 400 yards at -10º

don't know any metallurgy at all, so I've no idea what the difference between a Barnes or Swift would be compared to bullets with various gilding metal jackets WRT temp differences.

the pattern repeats with a 200 yard zero - about 2" difference at 400 yards, and a shade under 5" at 500 yards.

 

[C.W. Richter]

at 90º F
View attachment 451813

at -10ºF
View attachment 451814

still no appreciable difference until 400 yards at -10º

don't know any metallurgy at all, so I've no idea what the difference between a Barnes or Swift would be compared to bullets with various gilding metal jackets WRT temp differences.

the pattern repeats with a 200 yard zero - about 2" difference at 400 yards, and a shade under 5" at 500 yards.

in each instance, it was using Nos PTs in a high pressure WSM case. I have NO idea if the bullets come apart, etc. as they didn't even hit the target (but that flat base w/ the exposed lead/jacket contact makes one wonder). So, it's finicky powder (still a poss! not factored into a simple ballistics calculator), the gun and/or the bullet. Shots were not rushed, steady rest/aim. I intend to try and sort it out before winter ends (it's too warm today 29F). LOL

 

[sgt_zim]

we don't get a lot of temp variability around here, not enough to test with anyway. it's usually hot, or a bit less hot, with a few nights of temps in the 30s, maybe 1 or 2 down in the 20s.

my deer camp in Louisiana is ~85 miles further north than where I live, Falls and Winters aren't cold, but they are generally quite a bit colder there than here, where it'll dip down into the 20s with regularity, and teens occasionally. this year, I probably spent 40 days in the woods. ~35 of those were days where the low temp never got below about 60 or 62

 

[C.W. Richter]

Here's an approximate representation using the conditions I'm facing. Precisely 100 f range in temperatures the effect of that on the powder and the ballistics as well as all the metals involved. As I recall the couple misses were at just under 300 yards to 450 yd. (The gun was checked afterwards and the hundred yard print was fine.) The differences are not insignificant under these conditions coupled with elevation and humidity differences, etc. But I def have to sort it out in one particular gun! It is interesting to note that simply under these temperature conditions with this particular load it's nearly a 3-in difference in 200 yd. Not a big deal for
until the longer range shot presents itself... Things that need to be examined prior to going after the big white tail you've been chasing after all year or worse yet ibex argali NA sheep or even 300m+ Target shoots.

 

[BrenGun]

Not sure if already stated, but I notice when sighting in my rifle, it may take a number of shot to finalize - thus heating the barrel. Before a hunt, perhaps a month or two later, I’ll revisit and take a shot or two just to be sure. Always seems to shoot higher - Cold barrel? Drives me crazy.

Hi Fixfire

Yes I agree, I make sure I put a round through the barrel 1st. I wont zero a cold bore
Cheers

 

[gbflyer]

Set POI dead on at 100 meters then the 2” elevation change between sight - ins won’t bother you.