Temperature sensitivity of US869

[Michael Eichele]

I am headed out tommarrow to do some load development. While I am there, I was going to chrony some loads with US869. It has been about -8 degrees here and thought that would be perfect to keep some loaded ammo out side over night and some in the house at 68 degrees, chrony them and note the differance. I will post agian tommarrow after this test. I will be testing this in a 300 RUM with 180 ACCUBONDS.

Has anybody tried this already and if so, what did you conclude?

 

[Buffalobob]

Not at those temperatures.

But the difference between 65F and 95F is pretty radical.

 

[CatShooter]

[ QUOTE ]
"... I will post agian tommarrow after this test.

[/ QUOTE ]

Looking forwards to your results.

 

[jmden]

+1

 

[Hired Gun]

It's going to be big. I have watched Varget, IMR-7828, RL-25, RL-22, Retumbo, H1000, H-380, IMR-4350 IMR-4831 plus other so called temp stable powders all at one time or another started chronographing in the morning on through the mid day heat and you can watch the velocities go up as the heat increases. In my 100 round boxes I carry for my long range 300Wby I am thinking of loading up 10 each for each temp range to keep my velocity as close to 3100 fps as possible. I use a custom BDC dial on my scope and it is imperative I keep my velocity constant. Back in the olden days I didn't shoot over 400 yards much and 100 fps one way or another didn't ever make any difference while shooting game.

 

[41mag]

In one very limited test, we shot three loaded with 92 grs at 98 degrees F. then followed up with three of the same which had been put into a cooler and brought down to 60 degrees. The net finding was about 250 fps of velocity loss for the colder ones.

So far this has worked somewhat along with our drops and the Exbal we set up for our rifles.

I am definately interested in what your going to get on the lower temps.

 

[Guest]

[ QUOTE ]
In one very limited test, we shot three loaded with 92 grs at 98 degrees F. then followed up with three of the same which had been put into a cooler and brought down to 60 degrees. The net finding was about 250 fps of velocity loss for the colder ones.

[/ QUOTE ]
A++ work/data. The approach is not perfect (at 60 deg the air in the pipe will be denser) - denser air would lower the velocity even more (but probably less than 3%). What a great idea - work up a velocity/temp data chart.

 

[davewilson]

i only tested one round last year, it chronod the same.but this would be in of the 5 i keep in my pockets and they seem to impact where they should.that's how i deal with the changing temps.

 

[Michael Eichele]

[ QUOTE ]
In one very limited test, we shot three loaded with 92 grs at 98 degrees F. then followed up with three of the same which had been put into a cooler and brought down to 60 degrees. The net finding was about 250 fps of velocity loss for the colder ones.


[/ QUOTE ]

This is quite a bit differant from what I found. Granted, I was using a barrel within a stable temp range and these tests were NOT done with a fridged barrel. I dont know if that makes a differance or not.

Here is what I found:

104 grains of US869 under a 180 ACCUBOND. Powder temp around 67 degrees vs. the same except the powder temp was -7 degrees. The differance was right at about 120 FPS. Thats for 74 degrees of differance.

95 grains of H50BMG in the same scenario was about 74 FPS.

For all of you that hate the RL line, the colder one was faster by 33 FPS! Dont ask me why.

There was one other post here that had similar results.

http://longrangehunting.com/ubbthreads/s...=true#Post91531

 

[CatShooter]

[ QUOTE ]
... The approach is not perfect (at 60 deg the air in the pipe will be denser) - denser air would lower the velocity even more (but probably less than 3%). What a great idea - work up a velocity/temp data chart.

[/ QUOTE ]

Big Bore...

You have taken the art of silly to new, all time heights.

If you want to count the angels on the head of a pin, you must first know the size of their shoes, the size of their waist, and the size of their bra...

Air at 59 degrees "F" = 1.2 grams per liter (1000 cc) or 0.0012 grams per cc or 0.0185 grains per cc @59 degrees

At "0" degrees "F" - 0.0209 grains per cc

Volume... 1 cubic centimeter = 0.061 023 744 cubic inch

volume of .308x26" barrel = 0.6166 cubic inches

Therefore the weight of the air in a 30 cal barrel that is 26" long (NOT including the chamber) is 0.001128939819 grains at 59 degrees and 0.0012753968766 grains at "0" degrees, or a whoppin' 0.0001464570576 grain difference in the weight of the air in the barrel from 59 degrees to "0" degrees.

I think (in my humble opinion) that 0.000146 of a grain weight difference in the weight of the air in the barrel will not make a difference in the velocity... since it is about 1/1000th of the weight difference between bullets of the same lot number /ubbthreads/images/graemlins/wink.gif /ubbthreads/images/graemlins/wink.gif

 

[41mag]

meichele,

When we tried the temp check, the ambient was pushing close to 98 and we had 100% humidity. We had been load checking a few different powder charges and figured that since we had the drink cooler with us we would try the test. We stuck three rounds in the cooler, for about 30 minutes. After we put them in the cooler, we put three consecutive rounds of the ambient temp loads through the chrono. After letting the barrel cool and the three in the coller reach the ambient temp of the cooler, we fired them through as well.

Granted this wasn't too awefully controlled, but it was something that has repeated since the weather has cooled somewhat down this way.

Bear in mind, down here where we are shooting it is generally in the 60% humidity levels and we are at most only 170ft above sea level. Our max loads with the 869 or the 872 generally run somewhere in the range of 5 - 9 grs below what most can get, before we start getting pressure signs. Yes we can run the loads up to about 98grs with the 169.5 but then the cases only last about three loads before being trash.

Just thought I would throw in what we have found.

 

[RockyMtnMT]

I am pulling this up from the deep catacombs to see if anyone has anything to add to this thread. Would like to hear experience with US869, WC872, and WC860. Experience with over bore top pressure loads in different temps would be helpful. I have been experiencing some pretty big pressure increases with 869 and top loads with only 20 deg temp increase.

Steve