Temp sensitivity...

[wildgene]

...article in Rifle Shooter...

http://www.rifleshootermag.com/accuracy ... nsitivity/

...I do know that smaller cases tend to show more temp. sensitivity, & that it's a curve, not a straight progression. A load developed @ 65* fired @ 105* will show a lot more variance in MV than the same load fired @25*. I use the Sierra Infinity ballistics program that allows me to adjust the parameters for temp, humidity, elevation, barometic pressure, etc., to match my Density Altitude, & I spend way too much time twitching & tweeking loads, but the truth is, the actual shift in POI is pretty marginal, & my time would be better utilized practicing shooting from field positions...

 

[DrMike]

Excellent summary of a controversial topic, Gene. Thanks for posting the article.

 

[Guy Miner]

Learned a lot about temp sensitivity when I was competing in NRA mid & long range rifle matches. Goodness...

I'd work up a good 600 yard load for my .308 Win in the winter or spring. It shot just fine. Then some hot summer day, it would be shooting much faster & flatter. I'd have to dial back the elevation on the sights to keep the rounds impacting in the black.

One time, using some VV powder, I ended up ruining some rather spendy Lapua cases as the pressure got too high! The load shot well, but was hot & fast. The primer pockets were so enlarged that I had to toss the cases. Phooey.

Actually had some factory loaded Winchester match ammo that got all goofy on me in the summer too. Accurate, but loaded hot. It did NOT like high summer temps.

Guy

 

[Horsethief]

One revealing item in the story is that the change with temperature insensitive powder is not enough to make a huge difference inside of 400 yards. Ho hum, so the changes we thought we were experiencing aren't that bad. On the other hand, shooting in hotter temperatures with loads worked up in much lower temps didn't do so well----in case life, accuracy / elevation changes, and anything else I can't remember right now.
I use RL-19 and Hodgdon extreme powders, so the issue isn't that bad for me.

 

[Osprey78]

Whether it makes a difference or not, I made the switch over to non temperature sensitive powders about a year or so ago. In my head, I find that if I can eliminate that one Possible variable, all the better for me.

We reload here and it can be -20C. When we hunt in the early fall it can be +20C or higher. That's quite a temperature difference.

 

[Ridgerunner665]

Temp sensitive powders aren't exactly a deal killer...as long as you are aware of how they affect trajectory...todays ballistics software (Shooter, Applied Ballistics) allow you to enter the velocity change per degree into the program...after that, don't worry about it.

I do try to stay away from powders that show more than 1.3 fps change per degree of temperature though...most are around 1.3, but many of Alliants powders are pretty bad, as are Accurate powders, and a couple of IMR as well.

And the powders behave differently in different rounds...Reloder 22 in the artticle above showed almost as bad a change as it did for me when I tested it in 300 WM a few years back...it was a tad over 2 fps per degree in the Win Mag.

Same for Hodgdens Extreme powders...in some rounds they work awesome at temp stability, in others, they are just OK...H4350 works AWESOME in 30-06, but is just OK in 270.

At 1.3 fps per degree...for hunting purposes, you're good to go to 600 yards...no need to worry about it at all, it will be within 3-4 inches for both drop and drift at temps between 0 and 95 degrees.

 

[Dr. Vette]

Temp sensitive powders aren't exactly a deal killer...as long as you are aware of how they affect trajectory...todays ballistics software (Shooter, Applied Ballistics) allow you to enter the velocity change per degree into the program...after that, don't worry about it.

I do try to stay away from powders that show more than 1.3 fps change per degree of temperature though...most are around 1.3, but many of Alliants powders are pretty bad, as are Accurate powders, and a couple of IMR as well.

Where do you find the data on the temp sensitivity of a powder? I can't say that I've noticed it on the bottle or anything, but I have seen where I can enter it in Shooter as you note.

 

[Ridgerunner665]

Temp sensitive powders aren't exactly a deal killer...as long as you are aware of how they affect trajectory...todays ballistics software (Shooter, Applied Ballistics) allow you to enter the velocity change per degree into the program...after that, don't worry about it.

I do try to stay away from powders that show more than 1.3 fps change per degree of temperature though...most are around 1.3, but many of Alliants powders are pretty bad, as are Accurate powders, and a couple of IMR as well.

Where do you find the data on the temp sensitivity of a powder? I can't say that I've noticed it on the bottle or anything, but I have seen where I can enter it in Shooter as you note.

You have to map it out yourself...shooting at different temps and taking notes of the changes....its easiest with a chrono, but can also be reverse engineered with some degree of accuracy using a program like QuickTarget.