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gun powder win 231 temperature sensitivity


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Anyone know how big a jump the velocity would change as a result of temperature change, particularly those using win 231


What I am after is if I have a load that produces a 990 fps on a 40 S&W 180gr projectile during winter at 8 degress,  Will the velocity go up when outside temperatures are say 36-38 degress?





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I did some temperature variation testing of W231 with Acme 180gr FP-NLG bullets in the spring of 2017.


I used Hot-Hands heat packs to raise the temp of the magazines to about 100 deg F, ice packs to drop the temp to about 30 deg F and the ambient temp was about 40 degF.  Mags were loaded and placed in separate coolers (or left out for the ambient testing) about an hour or so before leaving for the range, which is about 30 minutes away.  I used an IR thermometer to measure the temp of the top round of ammo in each magazine before running the ammo from that mag over the chrono.  The mags were surrounded by the hot/cold packs with the top round in "free air" above the packs within the insulated containers.


I saw an average of 1-2 FPS per grain of powder difference between 30 deg F and 100 deg F.   With the 4.72 gr of W231 in these rounds, that resulted in velocities of 930 FPS (avg) at 30 deg F and 935 FPS (avg) at 100 deg F.  This equates to about 1 PF difference.


I no longer worry about temp sensitivity with W231. 😎


Blue Dot, on the other hand... which I load in my 9mm ammo and tested at the same time... is inverse temp sensitive and it will lose almost 100 FPS (13 PF) over the same range!  146 PF @ 30 deg F and 133 PF @ 100 deg F!  🥶😱

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