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Effects of Humidity / Temp on Reloads


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I've got my load worked up for meeting SSP power factor in IDPA. Out of 10 rounds I'm averaging 135.46PF which is just about 10.5 over the required 125. I dont know, if I'm being overly paranoid about being chrono'd at major matches (I'm shooting Razorback in AK on the 18th) and I'm curious how much of "buffer" (if you will) to account for temp/humidity, I should allow for or what the general consensus is, for what it should be.



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Most set power factor to be at least 5 higher than minimum. Then adjust higher for accuracy and comfort levels. 

Many of powders used, there are exceptions and WST is one of them, go faster as it warms and slower as it cools.


I think most load minor to an average of 130-135. If you do this I would not worry about being below PF.


The goal is consistent accuracy, and return of the sights (recoil); not the softest shots. 

Personally my minor PF averages 133.  

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How much of a margin you need is wholly determined by how consistent your load performs.  If the SDs are low you can get away with less.  If high you'll need more headroom.


For example, my major 9mm load makes and average of 169 PF.  I can get away with that because the slowest round in a 15 shot string makes 168 PF.  When I first started I shot Limited, then switched to 40 Open.  I made a very consistent loads at 172 PF, because that's what everyone said to do.  They made 172 at the chrono station.

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