Temperature sensitivity in ambient temperature

[Gil P.]

I've seen tests done where people put ammunition inside a freezer and shoot it, then shoot some ammo that was left out to warm up in the environment.

Do these tests hold any water? For instance: using H4350 I noticed that my velocity varies greatly depending upon the ambient temperature. I have recorded it as varying slightly over 1fps/degree. This is using the same lot of powder and primers.

I just recorded 6.5x47 Lapua cartridges loaded with 40.5gr H4350 at 2870 fps out of a 26" barrel. I'm going to keep some of the cartridges for a month or two and record the difference in velocity. This way I will eliminate any variables in the cartridge.

What have your findings been?

Measuring every charge with an FX120i, not weighing bullets, cases, or primers. Using 140 Berger Hybrids. Chrono is a Magnetospeed Sporter.

 

[spife7980]

What have your findings been?

The same as everyone else who has ever done it, they go faster when its warm, they go slower when its not.

And its powder temp that matters, not ambient temp.
Cold powder in a hot chamber will still be cold powder for a bit until you let it soak up the heat from the chamber.

 

[Gil P.]

I did my above mentioned experiment.

First test on 3/15/20 - temp 66*, 2870 fps avg

Second test on 5/16/20 - temp 79*, 2901 fps avg

Fps/degree change is .42 fps.

It seems like a lot for this powder.

I don't recommend letting your 140s reach 2900 in 6.5x47 Lapua. I've since backed it down to 40.1gr H4350 and am getting a much safer 2848 fps avg

 

[never_summer]

That may be a little high for h4350 but not really bad temp sensitivity, .42 fps/deg. How many rounds did you shoot and what are your es/sd for the rounds? There’s plenty of info out there on temp sensitivity and general gain/loss per degree for most powders

 

[Gil P.]

The first time around I think it was 15- 20 rounds. SD is usually between 9-12 with that load.

The second time I only shot 4 rounds, es was around 15-20. The bolt lift got a little stiff at that speed.

 

[Deleted member 113831]

Temp sensitivity isn't just determined by the powder. Case capacity, bore volume, bullet weight, primer sensitivity, all play significant roles.

H4350 in a 6.5 Creed or 6.5x47 will act differently than the same powder in a 30-06.

The change is also variable depending on the temp range. 0-40* won't show much change. 40-70* will show a bit more...and nothing good happens above 80*. All powders become temp sensitive above 80*.

.4 fps per degree is average from everything I've seen and read in cases of the size you are using.

 

[Gil P.]

I heard that RL 16 is more stable at high temps. I'm going to try it on my next barrel.

It's above 90 where I live for close to 5 months out of the year.

 

[Ajrich]

I heard that RL 16 is more stable at high temps. I'm going to try it on my next barrel.

It's above 90 where I live for close to 5 months out of the year.

Just saw a chart where R16 was the most stable with averaging 0.10° per degree, retumbo was next

 

[pell1203]

I did my above mentioned experiment.

First test on 3/15/20 - temp 66*, 2870 fps avg

Second test on 5/16/20 - temp 79*, 2901 fps avg

Fps/degree change is .42 fps.

It seems like a lot for this powder.

I don't recommend letting your 140s reach 2900 in 6.5x47 Lapua. I've since backed it down to 40.1gr H4350 and am getting a much safer 2848 fps avg

I’m a little confused here... wouldn’t Fps/degree calculation be:

(31 fps/13 degrees) = 2.384 fps/1 degree

Seems like the 0.42 number being used above is:

(13 degrees/31 fps) = 0.419 degrees/1 fps

It seems more logical to me to express the relationship as fps/degree but I understand the calculation of degrees/fps is also valid and as meaningful. Just a ratio being expressed in different units.

Is the latter form (degrees/1 fps) just the more accepted format? Am I missing something more meaningful here?

 

[Deleted member 113831]

I’m a little confused here... wouldn’t Fps/degree calculation be:

(31 fps/13 degrees) = 2.384 fps/1 degree

Seems like the 0.42 number being used above is:

(13 degrees/31 fps) = 0.419 degrees/1 fps

It seems more logical to me to express the relationship as fps/degree but I understand the calculation of degrees/fps is also valid and as meaningful. Just a ratio being expressed in different units.

Is the latter form (degrees/1 fps) just the more accepted format? Am I missing something more meaningful here?

You are right. OP did his math backwards.

 

[Milo 2.5]

Just saw a chart where R16 was the most stable with averaging 0.10° per degree, retumbo was next

Not dismissing what you say, but this seems to depend on individual tests. For yrs Varget was the king, Retumbo not even an honorable mention.

 

[Ajrich]

Not dismissing what you say, but this seems to depend on individual tests. For yrs Varget was the king, Retumbo not even an honorable mention.

I agree, I saw a test done between H1000 and Rl26 showing H1000 was much better. This test shows RL26 is better.

 

[Milo 2.5]

I've seen tests done where people put ammunition inside a freezer and shoot it, then shoot some ammo that was left out to warm up in the environment.

I am not a big fan of using ammo coming from a freezer test, I don't know why. The only true test is shooting ammo that is the same as ambient temps IMO.
A few around here were bragging on their powder of choice, story was -40 to 140 degrees. Well, a freezer wont get you to -40, and the temp has never dipped to -40 in the 40 yrs I have lived here. The 140 degree claim, not sure how that number came up either, unless a temp gun was used, highest temp recorded here in 40 yrs again has maybe been 103 degrees.
What I am saying, IMO, most tests I hear about are someone trying to prove one powder is superior to another, then another runs a similar test with opposite results, I just have no faith in many tests.
Not sure what the criteria is for an extreme designation from Hodgdon, but I had a couple Dashers built for kids, running H4895, 105 hybrids. All I can say is, when you hear the 1K benchrest game is about tuning throughout the day, it is an understatement.

 

[CoryT]

Case fill, primer, actual volume of powder all play a role as well. Just because you get good results with Varget in a .308 does not mean you get the same results on a 6.5 Grendel.

Cold soaking in a freezer is fine, but it takes at least overnight. I'm more skeptical of a heat gun, but you can use a warming system is you place an instrumented round in to get the actual core temp. This involves inserting a themocouple in the primer hole to the center of the powder column to read the temp. Measuing the temp of the case with an IR thermometer is going to deliver poor results.

 

[Gil P.]

I’m a little confused here... wouldn’t Fps/degree calculation be:

(31 fps/13 degrees) = 2.384 fps/1 degree

Seems like the 0.42 number being used above is:

(13 degrees/31 fps) = 0.419 degrees/1 fps

It seems more logical to me to express the relationship as fps/degree but I understand the calculation of degrees/fps is also valid and as meaningful. Just a ratio being expressed in different units.

Is the latter form (degrees/1 fps) just the more accepted format? Am I missing something more meaningful here?

Thanks for correcting me, I had that backwards for sure.

So my observed fps/degree change is 2.384 fps. That is really terrible. It makes me think that my test is meaningless,and maybe it is, and maybe most other tests too.

It seems like everyone gets different results.

 

[Gil P.]

Case fill, primer, actual volume of powder all play a role as well. Just because you get good results with Varget in a .308 does not mean you get the same results on a 6.5 Grendel.

Cold soaking in a freezer is fine, but it takes at least overnight. I'm more skeptical of a heat gun, but you can use a warming system is you place an instrumented round in to get the actual core temp. This involves inserting a themocouple in the primer hole to the center of the powder column to read the temp. Measuing the temp of the case with an IR thermometer is going to deliver poor results.

In my tests, I left my ammo in the garage overnight, drove them to the range and then let them sit in the shade for about an hour before I shot them.

 

[Gil P.]

I am not a big fan of using ammo coming from a freezer test, I don't know why. The only true test is shooting ammo that is the same as ambient temps IMO.
A few around here were bragging on their powder of choice, story was -40 to 140 degrees. Well, a freezer wont get you to -40, and the temp has never dipped to -40 in the 40 yrs I have lived here. The 140 degree claim, not sure how that number came up either, unless a temp gun was used, highest temp recorded here in 40 yrs again has maybe been 103 degrees.
What I am saying, IMO, most tests I hear about are someone trying to prove one powder is superior to another, then another runs a similar test with opposite results, I just have no faith in many tests.
Not sure what the criteria is for an extreme designation from Hodgdon, but I had a couple Dashers built for kids, running H4895, 105 hybrids. All I can say is, when you hear the 1K benchrest game is about tuning throughout the day, it is an understatement.

I have loaded 308 ammo using RL 15 here in Las Vegas, then went to shoot a PRS match in Washington where it was snowing and was about 20*. I didn't adjust my powder load or chronograph my bullets, but I was still hitting targets just fine out to 800-900 yards.

The temp in Vegas that month varied between 70 - 90 degrees.

Again, it doesn't mean anything, just another anecdote.

Maybe it's wrong to think that "temperature insensitive" powders should be a criteria when selecting a powder.

 

[Milo 2.5]

I have loaded 308 ammo using RL 15 here in Las Vegas, then went to shoot a PRS match in Washington where it was snowing and was about 20*. I didn't adjust my powder load or chronograph my bullets, but I was still hitting targets just fine out to 800-900 yards.

Maybe it's wrong to think that "temperature insensitive" powders should be a criteria when selecting a powder.

Now I am not in disagreement here, but were you center punching these plates? I have said for yrs, any decent shooter after a couple shots can make adjustments on the fly, either with a turret or a hold.
I think hunters need to be more cognizant of stability than say myself. Even if they develop in the fall, small window, and the possibility of huge temp swings can occur in the fall during the day.
I have shot RL 17, VV N 500 series, Norma powders, none known for stability and never had the issues I read about. Honestly today, I tend to buy stable powders, but if need be, I will shoot what is available that works.
There are only 2 powders I have found unacceptable in WY climates if you don't want to play the calc game every outing, CFE 223 and VV 20N29. I am sure there are more, or someone to prove me wrong.

 

[Gil P.]

Now I am not in disagreement here, but were you center punching these plates? I have said for yrs, any decent shooter after a couple shots can make adjustments on the fly, either with a turret or a hold.
I think hunters need to be more cognizant of stability than say myself. Even if they develop in the fall, small window, and the possibility of huge temp swings can occur in the fall during the day.
I have shot RL 17, VV N 500 series, Norma powders, none known for stability and never had the issues I read about. Honestly today, I tend to buy stable powders, but if need be, I will shoot what is available that works.
There are only 2 powders I have found unacceptable in WY climates if you don't want to play the calc game every outing, CFE 223 and VV 20N29. I am sure there are more, or someone to prove me wrong.

I shot this particular match back in 2014, I didn't make any adjustments to my drop data and held center plate and left or right for wind.

It was tough to see where my bullets were hitting. Back then I was using a fixed SWFA 12X.

 

[Gil P.]

I think I have a bad lot of powder. I don't know what else could be happening.

It's 104 degrees today in the shade and my velocity went up to 2970 using the same batch of cartridges I loaded the last time I shot. This stuff is dangerously temperature sensitive.

Im going to pull all my bullets and start over with RL 16.