Superformance Temp Sensitivity

General RE LEE

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I had a great day at the range with Superformance out of my 6.5 CM. I got .2” group with 130 grain Berger OTM 2828 FPS and .3” group 140 grain Sierra Tipped Game King 2901 FPS. Both loads had SDs around 9-10 and ES under 20. This is a hunting rifle.

Temps today were 85 degrees. With 2828 fps out of 130 Berger OTM and 2901 out of 140 grain Sierra tipped Game King with Superformance, how much velocity loss can I expect this November and December in Tennessee 25-50 degrees hunting temperatures?
 

CMP70306

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Sep 12, 2011
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When I used it in the PRC it was around 150 fps from 30 to 80 but I found out the other way. I loaded them to 3150 fps during hunting season but when to shot them in the summer they spiked to 3300. I loaded it for years in the 30-06 but never noticed because I only ever shot those rifles in winter and I didn’t have a chronograph at the time.
 

BallisticsGuy

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Why don't you test it. Drop some rounds in a baggie in a cooler full of blue ice packs, take to range, shoot over chronograph and don't fart around trying to hit the target while you're at it. Pull the round from the cooler, shoot it quickly, rinse and repeat for at least 5 shots. I do testing for my students as a matter of routine and depending on the powder, case capacity and other factors we'll see anywhere from .2fps per degF to 2fps per deg but there's often a sort of stable area, usually in the 40-80f range where things are pretty stable. If you do a hot test too (leave some ammo on the dash when it's warm out or use ThermaCare or similar hot pads to warm some up to 110-130F) then you can draw something of a slope and adjust your inputs on your ballistics calculator when appropriate.
 

rbTanzan

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Sep 11, 2012
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Why don't you test it. Drop some rounds in a baggie in a cooler full of blue ice packs, take to range, shoot over chronograph and don't fart around trying to hit the target while you're at it. Pull the round from the cooler, shoot it quickly, rinse and repeat for at least 5 shots. I do testing for my students as a matter of routine and depending on the powder, case capacity and other factors we'll see anywhere from .2fps per degF to 2fps per deg but there's often a sort of stable area, usually in the 40-80f range where things are pretty stable. If you do a hot test too (leave some ammo on the dash when it's warm out or use ThermaCare or similar hot pads to warm some up to 110-130F) then you can draw something of a slope and adjust your inputs on your ballistics calculator when appropriate.

This is a good approximation, and useful, but this does not change the temperature of the barrel nor will it necessarily approximate the POI change.

In other words, if there is a 100+fps velocity change you can expect a POI change as well and you will need to sight-in again during the other temperature season. But you will know the muzzle velocity, approximately, maybe +/- 25fps.
 

Mike Matteson

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Jun 26, 2017
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If short range it probable won't be much difference, but longer yardage yes it will change the POI. To answer your question easly look at a bullet in fight chart to see what 100fps does at longer ranges. That not the total picture, but will give you an idea as to whats going on.
 

rbTanzan

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Sep 11, 2012
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If short range it probable won't be much difference, but longer yardage yes it will change the POI. To answer your question easly look at a bullet in fight chart to see what 100fps does at longer ranges. That not the total picture, but will give you an idea as to whats going on.

The change is normally more than trajectory for +100fps. Velocities interact with barrel harmonics differently because they leave the muzzle at different barrel "wiggles".
Some rifles shoot loads to many different spots. I've shot rifles that spray different bullets over 10-12 inches. Such a rifle will be sensitive to different speeds as well as different weights of bullets. A person will need to see how a particular load shoots, and at different velocities even at 100 yards.
 
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