We had a shooter using a Remington 40x .243 win last Saturday... he had his drop chart marked for 32.5 MOA at 1040 yards... (pretty flat shooting cartridge)... he was using a Hornady 100 grain Spire Point boat-tail, and 40 grains of IMR 4350.
As the day wore on... we experienced a temperature drop of about 15 degrees. When we went back to that target, he needed nearly 34 MOA to center it again.
So it indeed appears (anecdotally anyway) that the IMR 4350 might be a little fussy about the temperature. And I do say "might be" as I've not really tested or proven the issue. Other guys claim over 100 fps of velocity loss from 80ish to freezing... and it could be the case.
Even if the IMR 4350 load did lose around 50 fps (which is what the drop change would have indicated) that doesn't mean it would be a linear drop all the way down the thermometer. We saw temps go from around 75 degrees to around 60 degrees... that's when the difference seemed to pop up. Could have been something else though, so I can't emphatically say it was the powder.
Just adjust your drops to match reality in the temperature you're working in. There are of course more temperature stable powders available, but I'm a fan of the old IMR powders because they're so consistent lot to lot... unlike Hodgdon's "extreme" rated versions.
I haven't shot a lot of IMR 4350 at long range until recently... I use it in my .270 with 150's (52.5 grains) and it works great... but will need to check its behavior at long range next time I get the chance.
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Last edited by Dan Newberry; October 7, 2012 at 11:34 PM.