Temperature sensitivity.. is it a big deal?

OP
allstajacket
Joined
Dec 2, 2022
Messages
352
Location
Southest Michigan
I wouldn’t worry about it at your intended ranges. A quick run of the numbers in Applied Ballistics gave the following:

165 accubond at 2650 fps MV at my current station pressure: 7.75 MOA at 400 yards (100 yard zero).
165 accubond at 2600 fps MV at my current station pressure: 8.00 MOA at 400 yards (100 yard zero).

An elevation impact difference of about 1 inch for the 50 fps MV difference.

This is just about a worst case scenario at your longest anticipated range and a pretty big temp difference.

Thanks for this rundown. I think I’ll try out imr4064 and varget and use whatever works!


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Gingerman

Lil-Rokslider
Joined
Nov 24, 2022
Messages
273
My experiences to fill in any gaps not already understood...I got ultra nerdy for a decade or so examining the relationship between atmospherics and velocity.

Powders, whether stick or ball, will only be affected so much by the cold until they plateau at a certain velocity. If you load developed a bughole round at 75F your only worry is if an extreme cold condition has changed your harmonics to a 3 MOA shooting load. No safety concerns.

Safety concerns come in the opposite situation where load development produces an accurate & safe load in the cold and then that load is shot in the heat. There is no across the board plateau for powders in the heat, with one exception I'll mention soon. A ball powder like AA2520 loaded at 25F will go supernova at 105F. A Hodgdon Extreme line powder: Varget, H4895, H1000 etc will save your butt when shot in heat. Loads I developed at 65F increased velocity only 40fps when shot at 110F. No serious pressure signs. In contrast, I've recorded chrono readings with AA2520 giving 100fps increase and bad pressure signs at 85F.

You can also imagine my surprise when the loads I got dialed in like a champ in 25F wouldn't group at 75F. Still safe loads, but WTF happened? Well, it took me a bit, but I realized the cold kept my barrel cold/cool and eliminated a precision killer, HEAT! Barrel cold, rounds cold, small groups, happy times! (Taking pics run through the sub-moa app and sending to friends to brag and all that:))

SO, with all that said...I load Winter ammo and Summer ammo to beat the temp/velocity swings. Usually, that translates to Winter guns & Summer guns. (Hunting coyotes in 0-25F Winter, ELR range & hog shooting Summer.) This takes away some anxiety about the whole temp/pressure/precision matter.

Fun fact: You can load develop Summer loads in Winter should the need arise. I got a last minute invite to shoot hogs in a hot climate. I was experiencing freezing temps, and I was determined to shoot hogs with a new gun. So, I created a daggum sauna inside my truck cab, blasting the heat and rolling down the window far enough and long enough to shoot a single round. Rolling the rounds on the vents like hotdogs! Bwahahaha, that stupid shit worked too! I got to 100F property and slayed hogs with no pressure or precision problems!

Seek, gain, share knowledge. Then STFU! LOL
 
Joined
Nov 20, 2021
Messages
1,415
Over the top, but I'll be darned if I probably wouldn't have done the same thing had I even thought of that in my younger days.
 

N2TRKYS

WKR
Joined
Apr 17, 2016
Messages
3,954
Location
Alabama
When I started reloading years ago, it just made sense for me to only work uploads in the winter. I’m never gonna shoot in the summer, so I don’t care what it does then. I’m only loading hunting ammo, so I work my loads up during that temp. I’ve never had to worry about temp sensitivity.
 

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