Temperature sensitivity.. is it a big deal?

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I’m working on a load for my .308 to take to Montana this year for an elk hunt (165gr accubond) and I keep reading people talking about temperature sensitivity.

It seems like the general consensus on the internet is that Varget is the only choice to load for .308 and you are an idiot if you don’t…

Well I don’t have any Varget right now (have 2# coming next week) but do have AR Comp and IMR4064..

Is it really pointless to try to load with the powders on hand?

Is temperature sensitivity even going to come into play for me? I live in Michigan. I won’t be going anywhere where it’ll be 100° warmer, etc.


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Jr4

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It can make a surprising difference, Try Vihtavouri powders like N550
 
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I think there are many factors. Bottom line, when you get to your hunting destination, unpack a chrono, and verify your dope at distance. I think all powders have some burn ratio difference that would affect pressure/velocity depending on temperature and altitude, some like varget are very miniscule.
 
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AR comp is fairly stable IIRC. Lots of ways to skin the cat, there are just usually some proven easy buttons out there.
 

prm

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In my experience you can lose somewhere between 0 and 90 fps between 70 and 5-10 deg. depending on powder. The Hornady 4DOF software includes information on velocity loss per degree of temp change for a number of powders.
 
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allstajacket
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But if I’m hunting in 30-40 degrees, and I load/test my ammo in 30-40 degrees, will the sensitivity not matter?


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But if I’m hunting in 30-40 degrees, and I load/test my ammo in 30-40 degrees, will the sensitivity not matter?


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4064 will be perfectly fine in those ranges. I wouldn’t think twice about loading that up.

Temp sensitivity is primarily an issue at the far ends of the range. 0F and 100F. You aren’t that.
 

z987k

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4064 will be perfectly fine in those ranges. I wouldn’t think twice about loading that up.

Temp sensitivity is primarily an issue at the far ends of the range. 0F and 100F. You aren’t that.
It's only an issue with any powder if you're shooting at a fairly different temperature than you developed the load at.

If you load at 130F and shoot at 130F, it'll be the same.
 

SamsonMan22

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Even the 4064 won’t be too bad it seems to do well in a 308. All of my loadings with it have been made in 30-40 degree weather and up to around 70 degrees the velocity increase isn’t enough to change anything. In one rifle 90 degrees started to show a measurable increase in velocity but even the varget loads did there too. The 4064 loads in 90 degrees would put me out of the normal impact cone at 600yds. If I were shooting 1000yds I might think different but inside of the effective hunting range of a 308 the IMR 4064 will work just fine in a reasonable temp range. I actually prefer it to varget for all of the rifles I load for.
 

Wrench

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.....and a 308/165 means you're probably not shooting over 600ish.

Shorter range also helps even the spread.
 

SamsonMan22

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Correct. Max range would likely be 300-400 yards.


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Exactly at those distances an inch or two won’t mean a thing. I believe the federal gold medal match loads using the smk are loaded with a variation of IMR 4064 I think I read it has some sort of flash suppressant added, I can’t remember. Those are one of the loads I judge a 308 by if it won’t shoot 168 or 175 fgmm then that rifle isn’t going to shoot.
 

t_carlson

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Is it a big deal?

Yes and no, IMO.

Yes, it does exist, and could be a big deal in certain situations.

Is it as big of a deal as everyone makes it out to be? No. It was never a "problem" until temp-resistant powders came along. Now, with people shooting extreme LR, it could change impact.


Load your 308 with whatever is available and go to MT. Odds are, if you shoot an elk it will be <200 yards.
 
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IMR4064 is the powder of choice in my 35 Whelen AI. Good combination of velocity, filling the case and accuracy. Loads were developed at 70° temps, used below freezing for Colorado elk. It has always filled the freezer.

The real world implications at normal hunting ranges are pretty much nil.
 

Harvey_NW

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Certain apps have a sensitivity factor where you can input velocities at 2 different temps (the bigger spread the better) and it will compensate.
 

MattB

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AR comp is fairly stable IIRC. Lots of ways to skin the cat, there are just usually some proven easy buttons out there.
This

The internet can be a great place to gain information and learn. There is also a lot of poor and even untrue information on it which can cause some people to curious conclusions.
 
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There's a temperature stability chart for many powders out there on the internet. IMR4064 is .53 FPS per degree fahrenheit. Doing the simple math, from an 80° Day to a 10° day, just a bit over 35 fps loss.
 

Matt Cashell

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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.
 
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