Summer vs Winter velocities and temp stability

[Koda]

This weekend I had a chance to measure velocities on a handload recipe I developed last summer. I recall temps in the 80s on days I shot last summer. Today: high 42deg, 91%humidity, Elevation 1400', I got a chance to target shoot and sent 3 rounds thru my chrono out of curiosity and noticed it was less than I last recorded. I averaged them, and a difference of 41fps slower than last summer.
Does that sound about right?

Power is Accurate 2520.

Also does anyone have any kind of chart or info on temp stability for various powders or do we just go by what they claim?

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[Mono1]

This weekend I had a chance to measure velocities on a handload recipe I developed last summer. I recall temps in the 80s on days I shot last summer. Today: high 42deg, 91%humidity, Elevation 1400', I got a chance to target shoot and sent 3 rounds thru my chrono out of curiosity and noticed it was less than I last recorded. I averaged them, and a difference of 41fps slower than last summer.
Does that sound about right?

Power is Accurate 2520.

Also does anyone have any kind of chart or info on temp stability for various powders or do we just go by what they claim?

Bryan Litz touches on that subject in this video. It's pretty obvious Erik Cortina doesn't like Bryan Litz based on Erik's body language! Oh well!

 

[Koda]

Bryan Litz touches on that subject in this video. It's pretty obvious Erik Cortina doesn't like Bryan Litz based on Erik's body language! Oh well!

Im just gonna assume he says 41fps is about right or Im gonna cross my arms too...

 

[Mono1]

Im just gonna assume he says 41fps is about right or Im gonna cross my arms too...

I agree!

 

[Mono1]

Bryan sounds really smart.

But he has a tendency to talk a really long time without saying anything that helps me!

 

[Koda]

heres a link to a temp stability chart that kinda floats around reloading/gun forums. I dont see an official source for it to judge how legit it is but...
the number means the change in velocity for every degree of temp change...

powder temp stability chart

 

[Koda]

Bryan sounds really smart.

But he has a tendency to talk a really long time without saying anything that helps me!

my reply was my nice way of saying Im not going to watch that 1.5hr video to figure it out. He does seem pretty smart though I would probably trust him.

 

[American123]

This weekend I had a chance to measure velocities on a handload recipe I developed last summer. I recall temps in the 80s on days I shot last summer. Today: high 42deg, 91%humidity, Elevation 1400', I got a chance to target shoot and sent 3 rounds thru my chrono out of curiosity and noticed it was less than I last recorded. I averaged them, and a difference of 41fps slower than last summer.
Does that sound about right?

Power is Accurate 2520.

Also does anyone have any kind of chart or info on temp stability for various powders or do we just go by what they claim?

41fps sounds like a nearly insignificant difference considering the factors involved. Barely a difference. Must be considered a temperature stable powder.

However, there's a difference between cartridges that have been sitting in the cold for hours and are ambient temperature, and cartridges that got taken out of a warm house, rode in a warm car, and then were fired before significantly cooling down.

 

[Koda]

41fps sounds like a nearly insignificant difference considering the factors involved. Barely a difference. Must be considered a temperature stable powder.

However, there's a difference between cartridges that have been sitting in the cold for hours and are ambient temperature, and cartridges that got taken out of a warm house, rode in a warm car, and then were fired before significantly cooling down.

Thats my take, seems like a temp stable powder. 80deg - 42deg = 38deg difference is about 1fps per degree...

Thats a good point about cartridge exposure, though I do keep my cartridges inside a range bag to and from and out of the sun. Extra effort in the summer anyways.

 

[American123]

Thats my take, seems like a temp stable powder. 80deg - 42deg = 38deg difference is about 1fps per degree...

Thats a good point about cartridge exposure, though I do keep my cartridges inside a range bag to and from and out of the sun. Extra effort in the summer anyways.

Most powder manufacturers will list if they consider it temperature stable or not.

I forgot to ask what cartridge and what regular velocity.

 

[Koda]

Most powder manufacturers will list if they consider it temperature stable or not.

I forgot to ask what cartridge and what regular velocity.

I dont see anything on Hodgdons website for A2520, which leads me to the other question if there's a verifiable stability chart or something somewhere.

This is for my 6.5Grendel. I was testing some other powder today to see if I could get more velocity and ran 3 of my A2520 rounds thru to check winter velocities. Last summer my average was 2813fps with a 97gn bullet. Id like to keep my year round average above 2800fps but that doesnt seem to be possible with my powders.

 

[American123]

I dont see anything on Hodgdons website for A2520, which leads me to the other question if there's a verifiable stability chart or something somewhere.

This is for my 6.5Grendel. I was testing some other powder today to see if I could get more velocity and ran 3 of my A2520 rounds thru to check winter velocities. Last summer my average was 2813fps with a 97gn bullet. Id like to keep my year round average above 2800fps but that doesnt seem to be possible with my powders.

Alright. I don't have any experience loading that. But a 41 fps difference is between 1-2% change between temperatures. If you run that velocity difference against a trajectory calculator, you're probably not even going to notice it unless you are going for a very high degree of precision.

 

[DizzyJ]

I don't think that powder is considered temperature stable.

The extreme powders by hodgedon are supposed to be as well as Varget and a few others.

 

[Koda]

I don't think that powder is considered temperature stable.

The extreme powders by hodgedon are supposed to be as well as Varget and a few others.

According to the chart I linked to above A2520 is "fairly stable"...
But I dont know where that chart originated from, Id like to have a more authoritative source for that info but not certain its out there.

This was my first chance at checking temp stability (summer vs winter) so hopefully I can continue to add to my notes and share. I didnt think 41fps was that bad.

 

[Greg S]

I think IMR powders are affected more. Was taught in class for Federal 308 Match (168) to add an inch of elevation for ever 10° drop in temp on your 100 yard zero before adjusting for wind and distance.

 

[Stomper]

Stomper sounds really smart.

But he has a tendency to talk a really long time without saying anything that helps me!

Fixed it for you…..


Yer welcome!

 

[Mono1]

Fixed it for you…..


Yer welcome!

C'Mon Dude! YOU have some Valuable Insights.

I

Just can't think

of one at the moment.

 

[Xmark1]

This weekend I had a chance to measure velocities on a handload recipe I developed last summer. I recall temps in the 80s on days I shot last summer. Today: high 42deg, 91%humidity, Elevation 1400', I got a chance to target shoot and sent 3 rounds thru my chrono out of curiosity and noticed it was less than I last recorded. I averaged them, and a difference of 41fps slower than last summer.
Does that sound about right?

Power is Accurate 2520.

Also does anyone have any kind of chart or info on temp stability for various powders or do we just go by what they claim?

Years ago, I noticed that when shooting my 308, my POI changed about ten inches between summer and winter at 500 yards.

 

[Mono1]

Years ago, I noticed that when shooting my 308, my POI changed about ten inches between summer and winter at 500 yards.

Holy Crap! That is a Big Difference!

I was not aware of that. Thanks for the education!

 

[Koda]

Years ago, I noticed that when shooting my 308, my POI changed about ten inches between summer and winter at 500 yards.

Yes, understanding this POI difference is the goal. I also need to track POI shift with elevation changes but its rare I get to target shoot in another part of the state but eventually will take a trip.