Velocity changes due to temp?

[SDHNTR]

Theoretical academic question here… assuming a powder that is somewhat temp sensitive…

What effects velocity more, the temp of the barrel, the ambient temp, or the temp of the powder inside the cartridge? I know the answer is all of the above, but what has the greatest impact? Can you offset the effects? Say its 90 deg out and you are keeping the ammo cool in a cooler and not letting a round soak in a hot chamber long before firing? But that barrel is already warm and getting hotter. Are you gonna see likely faster speeds due to a hot barrel and warmer ambient temps, even though the ammo itself is cool at sub 40 degrees?

I need to shoot and it’s hot out! Just trying to draw some conclusions.

 

[Pickettpuncher]

In my mind, the barrel temp is the least factor. A hot barrel might kill your group. I do agree that you can keep your ammo cool in a cooler and it’ll cook in a hot chamber. What I’m not sure is how much ambient temp alone changes things. I would think ambient temps change what you see commonly published around the web, and a hot chamber makes it worse.

The biggest issue I see with a hot barrel is throat erosion is expedited and accuracy can/will suffer.

 

[Novahunter]

The answer will vary for different rifles, different powders, and different calibers.

Best thing to do is test.

In PRS, many of us do multiple tests on our loads which can also be helpful for a hunting load too. We water test loads for pressure. Many also test for temp fluctuations.

Go to a range on a hot day. Keep a bunch of rounds in a cooler with ice, keep a bunch of rounds in ambient air in shade, and let some cook in the sun for 30 min.

You aren't necessarily testing for group size differences. The data that's most important is velocity fluctuations, both ES and SD. If the ES and SD do not fluctuate greatly, then most likely your groups will not open up greatly. Pressure signs are also very important to watch for.

You can also heat your barrel up and let the rounds cook in the chamber for 30 to 60 seconds each to see effects on temp.

Make sure you have a good chronograph setup so you can capture reliable data.

When I've done these tests with with Varget and RL16, those were very temp stable and I did not see large velocity swings. RL 17 on the other hand showed high temp sensitivity (1fps change to every 1 degree change in temp). I'd recommend a Hogdon Extreme powder (Varget, H4350, Retumbo are in that family) as they generally exhibit great temp stability.

 

[SDHNTR]

Yeah, whenever I can get away with a Hogdon Extreme I love it, but what’s becoming my main rifle, I think, just loves H100v. Definitely seeing some temp changes. But it’s not always predictable. Which is why I’m trying to get a feel for other forces at work.

 

[PA Hunter]

I try to always sight my guns in before hunts with the temps I will be in. If this is not possible I bring a cooler to the range with ice packs and cool my rounds off before shooting. Last year I averaged 50-100 more fps doing testing in warmer temps compared to my rounds in the cooler. may not sound like much but my impact was a little different at 100 yds. I also let the barrel cool well between shots and really pay attention to the first shot the cold bore shot. Also rifle will not be cleaned until after the hunt. This is with my .300 RUM and handloads Retumbo powder.

 

[Coyote conquest]

I know ambient temp matters a lot but the temp of the powder may matter just as much. I'm not sure if ammo kept in a cooler that is 30 degrees will shoot the same as the ambient temp being 30 degrees though. Plenty of things on the net to read but I've never read of anybody testing it both ways
Humidity will most likely matter also. Moisture in the atmosphere will slow bullets down.

 

[SDHNTR]

I try to always sight my guns in before hunts with the temps I will be in. If this is not possible I bring a cooler to the range with ice packs and cool my rounds off before shooting. Last year I averaged 50-100 more fps doing testing in warmer temps compared to my rounds in the cooler. may not sound like much but my impact was a little different at 100 yds. I also let the barrel cool well between shots and really pay attention to the first shot the cold bore shot. Also rifle will not be cleaned until after the hunt. This is with my .300 RUM and handloads Retumbo powder.

I try to do that too. Though not always practical.

I did recently do some testing at 45 degrees (which is probably close to what I’ll be hunting in) on loads I had previously tested at 75 degrees. What was weird is the lighter powder charges sped up by 20- 30 ish fps and the higher charges slowed down by about the same, to where the lighter powder charge was actually faster than the load with .3 gr more powder. So now what? That’s what got me asking this. Head scratcher. Riddle me that one.

 

[N2TRKYS]

As long as it doesn’t show pressure signs, I don’t worry about it. My loads are usually in a node big enough that that little of a swing don’t matter.

 

[Rich M]

I dont notice any diff down here in fl. Velocity stays pretty constant. Using win 760 and lil gun mostly.

Barrel temp is the main concern to me due to grouping.

I bring a fan to cool down the barrel and wont shoot more than 5 in a row during summer. Dont like to shoot too much in hot weather tho. Get all sweaty and drip on the guns.

 

[Harvey_NW]

The temp of the powder should be the most linear relationship to velocity. The ambient environmentals will have the same affect they always do downrange, and can be calculated and compensated for. But based on the cold ammo test you should be able to develop an accurate sensitivity factor from the differences in velocity.

 

[SDHNTR]

Right, but why then did a smaller powder charge result in more speed than a slightly heavier charge? Some odd node preference for a slightly lesser charge is the only explanation I can come up with.

 

[Harvey_NW]

Some odd node preference for a slightly lesser charge is the only explanation I can come up with.

All shots out of a fouled barrel? Barrel temp the same or close? Not cooking in the chamber at all? Consistent amount of sunlight?

All things being controlled and equal I'd have to agree, some physical anomaly.

 

[ResearchinStuff]

A few years ago there was a thread somewhere about retumbo in sub zero temps having catastrophic overpressure and destroying guns using handloads that were safe in more comfortable weather. My takeaway from that thread was not all powders expand more rapidly at high temperatures, some can behave in the opposite manner.

 

[SDHNTR]

A few years ago there was a thread somewhere about retumbo in sub zero temps having catastrophic overpressure and destroying guns using handloads that were safe in more comfortable weather. My takeaway from that thread was not all powders expand more rapidly at high temperatures, some can behave in the opposite manner.

Now that’s interesting.

 

[SDHNTR]

All shots out of a fouled barrel? Barrel temp the same or close? Not cooking in the chamber at all? Consistent amount of sunlight?

All things being controlled and equal I'd have to agree, some physical anomaly.

Yes on fouled bbl. Bbl temp was close to same. Of course it warmed up some but I did my best to let it cool between 3-5 shot strings. Sunlight was consistent but I was also using a Magnetospeed.