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WST and temp velocity change question.


steel1212
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I know WST is reverse sensitive but my question is about how much velocity is lost when it warms up?

I'm at about 172pf (957fps x 180BBI) when it's 35 degrees. What about when it's 80-100? Looking for people who have actual results please not "that SHOULD be fine" lol

Edited by steel1212
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Using WST under a 147gr 9mm bullet, my summer tests compared to my winter tests were only between 3-4pf in difference. My notebook is at home, so I can't give you actual data this second. However it was not nearly as bad as I thought it would be based on hearing people complain about it.

"that SHOULD be fine"

:)

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I think people always talk about magazines sitting out in the sun though vs just being a bit warmer?

When you were recording the variances, was it just from bag to belt to shoot? Or was it out and getting HOT for some time.

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I have been using WST for about 10,000 rounds now and I think I got it figured out. The temperature of the round its self is far more important than the actual temperature of the testing environment. This is what I do to make sure that my WST loads will still make Major in really hot temps. I will artificially heat up the test ammo my laying it out in the sun or setting it on the heater vent in my car. Then I use an infrared temp gauge to make sure that my test rounds are 100+ deg F. Then I will load them up and chrono them immediately after taking them off the artificial heating process. I will load my ammo with a powder drop that still makes 167 PF in this artificially 100+ deg F heated condition. This ensures that no matter what match I go to (Super Hot shooting conditions) they will still make Major PF with a decent buffer. In the summer major matches with 80 - 90 deg temps the ammo usually ends up being 170 - 172 PF. The only time it was below 170 PF was at a match were it was 110 degrees and it was still making 166 PF, which is close but still good enough.

For me its too much brain damage to make "Cold Weather" rounds and "Hot Weather" rounds. I make all of my ammo work for Hot Weather conditions and just deal with the extra "Spiciness" the rounds have when its cold out. When the buzzer goes off you really can't tell a difference anyway.

To answer your velocity variance question, I have seen a 30 - 40 fps swing in velocity between a 30 degree round verses a 100+ degree round. At least with the 180gr FMJ's I am using.

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Another thing to consider is that "Usually" when you go to a major match and they capture your ammo for chrono its NOT sitting in a nice climate controlled environment. You have to account for the worse case scenario where your ammo may be sitting out in the sun right before you have to do the chrono. Some chrono guys will put the ammo in a cooler to keep the ammo temp from getting crazy hot, but that is not always the case. I remember attending one match where the chrono guy had everyone's ammo laid out on the ground in squad groups sitting in the sun. If you are using WST and don't account for something like that you may be upset by the chrono results.

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Like I said I doubt my ammo was actually 35 degrees since i set up the chronic then got my bag out and loaded one msg and shot. It proabably was at least 50ish. So if it's 50ish and 173 and I go some place that is 100 I should be good. I guess I'll find out down in Alabama this weekend where its going to be 80

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  • 2 months later...

Whats a najor? With your bullet if you are at or above 4.7gr of WST that will crono out at about 170pf at 100 if your barrel is of typical speed and your OAL is > 1.140 and <= 1.180. The only way to be sure is to crono it at the temp, artifical or real. And don't ride the line as the equipment, humidity, and altitude could just put you under.

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