Powder temp and case insulation?

[EXPRESS]

With the Shooter App you can add powder temp to your calculations, and it makes a huge difference to trajectory. Much larger than the atmospheric conditions.

However I don't find it to be accurate to the actual ballistics.

The Strelok Pro app lets you add a primary MV and then up to 4 more at different temps, so it can work out your powders' temp sensitivity. This seems to be a great method for establishing your actual variation, but I haven't had the opportunity to try it and verify it.

So I wonder if the cartridge casing offers some good insulation to the charge inside or are the powders I use just very stable?

 

[Schnyd112]

I was taught, when shooting strings for competition, to not chamber the round until I was ready to shoot. Line up on target, dope the scope, then chamber and shoot.

When the chamber heats up, it can heat the powder in a chambered round very quickly. I noticed a pretty significant difference when shooting my swift with hot loads of 4064. The extra time in the chamber finding the target would make the pressure would rise, my muzzle velocity would increase and it was hardly consistent shot to shot.

Not really an answer to your question, but real world experience in the theory.

 

[Timber338]

There are so many variables that go into temperature sensitivity. Of course the powders are proven to burn hotter/faster when they start out at a warmer temperature, and there are some established ranges of temperature sensitivity for each powder.

How large are the temperature swings when you are shooting? How are you measuring your muzzle velocity?

My motivation is first cold bore shot accuracy/velocity, so I go to great lengths to make sure my entire system is at the same ambient temperature on any given test so there are no variations. And then of course repeat the tests on different days that have warmer/colder ambient temperatures.

Based on my experience, I am very careful to shoot first thing in the morning, with the rifle and ammo being left outside all night. For the first hour or so of light, right as the sun is rising, I get a very consistent temperature window. I know everything is at the same temperature. And that is when I record a few shots in a row. Just like I would hunt with. So the whole point is, with the ammo just sitting in the air, I think the powder in the case will have some lag with the changing outside air temperature.

But just like Schnyd said, a cartridge in a warm bore, touching the chamber walls, can transfer heat to the powder very quickly.

So I think it could depend on your application for whether or not the powder inside the cartridge heats quickly. I think that bench rest shooters have an entirely different set of challenges than a hunter does. As long as you test appropriately, you should be able to characterize your rifle, because if your muzzle velocity is changing, your point of impact at long range will change accordingly.

 

[WildRose]

With the Shooter App you can add powder temp to your calculations, and it makes a huge difference to trajectory. Much larger than the atmospheric conditions.

However I don't find it to be accurate to the actual ballistics.

The Strelok Pro app lets you add a primary MV and then up to 4 more at different temps, so it can work out your powders' temp sensitivity. This seems to be a great method for establishing your actual variation, but I haven't had the opportunity to try it and verify it.

So I wonder if the cartridge casing offers some good insulation to the charge inside or are the powders I use just very stable?

No my friend about the only way you can add insulation is to use a magazine fed rifle and keep the magazine inside a pocket on the inside of your jacket or shirt pocket under the jacket.

The very nature of the brass casing is for extremely rapid transference of heat/cold.

Except in extremes of temperature, well below freezing and well above 100F I find it not to make a really big difference with most powders.

Some powders, typically the faster burning powders are extremely sensitive to temps to the point that if you are running maximum loads, leaving a magazine sitting in the hot sun or leaving your metal ammo can in the sun while shooting can warm them up enough for an otherwise safe load to start showing some pretty severe pressure signs.

With the extremes of weather where you are hunting I think I'd just ask for some of our more knowledgeable guys to give you a list of the least temperature sensitive powders so you can choose from them.

Hope all is very well with you and yours and I'm still planning one of these days to take you up on that invitation.

I'm having surgery on my lower back and right arm next week, and then again in October the other arm and my neck and once we get those out of the way I should be well on my way to being back in the kind of shape a guy needs to be in to enjoy huntin around the world again.

All the best. WR

 

[WildRose]

I was taught, when shooting strings for competition, to not chamber the round until I was ready to shoot. Line up on target, dope the scope, then chamber and shoot.

When the chamber heats up, it can heat the powder in a chambered round very quickly. I noticed a pretty significant difference when shooting my swift with hot loads of 4064. The extra time in the chamber finding the target would make the pressure would rise, my muzzle velocity would increase and it was hardly consistent shot to shot.

Not really an answer to your question, but real world experience in the theory.

And I was taught that an open chamber allows for a great deal of air flow and allows for pretty rapid cooling so like you, I won't chamber a round at all until I'm ready to shoot and I also always keep my ammo in the shade in warm temperatures and choose plastic or paper as my choices for what I keep my ammo in. Card board actually is a fair insulator and provides good protection from the sun and plastics do a pretty good job f both as well.

I've gotten to where I even prefer plastic magazines for my magazine fed rifles including my fairly substantial collection of tactical rifles.

 

[EXPRESS]

Yestrday I ran a temp test with the Magnetospeed.

First I left the rifle, kestrel and ammo outside, in the shade for a couple of hours. It was 18C which is nice mild spring day.
Got 2970fps avg.

Then I stuck the gear into my walk in chiller for a couple of hours. It was 4C which is pretty cold cold.
I quickly set up and fired three shots.
Got 2950fps avg.

So it seems the powder is sensitive by 1.6fps per 1C, which seems ok. I want to try it at around 30C which is a hot day, and also around -10 and see if the variation maintains linearity.

I just have to test drops now and find out where the error in my numbers was.

Wildrose, best of luck mate.

 

[RockyMtnMT]

Yestrday I ran a temp test with the Magnetospeed.

First I left the rifle, kestrel and ammo outside, in the shade for a couple of hours. It was 18C which is nice mild spring day.
Got 2970fps avg.

Then I stuck the gear into my walk in chiller for a couple of hours. It was 4C which is pretty cold cold.
I quickly set up and fired three shots.
Got 2950fps avg.

So it seems the powder is sensitive by 1.6fps per 1C, which seems ok. I want to try it at around 30C which is a hot day, and also around -10 and see if the variation maintains linearity.

I just have to test drops now and find out where the error in my numbers was.

Wildrose, best of luck mate.

What powder, load, and rifle?

Thanks

Steve

 

[EXPRESS]

Blaser R8 Pro Success
25" barrel
.338 win mag
74.5gn VV N160 CCI mag primer
CEB 225 LZR

 

[WildRose]

Blaser R8 Pro Success
25" barrel
.338 win mag
74.5gn VV N160 CCI mag primer
CEB 225 LZR

Nice rig, congrats on finally finding one that really suits you.

Looking at comparative burn rates the VVN-160 appears to be a pretty slow burner so I think you will get pretty good performance through the range of temperature extremes you hunt in.

Here's a pretty good burn rate comparison chart.

https://www.hodgdon.com/PDF/Burn Rates - 2015-2016.pdf

 

[Canadian Bushman]

My personal opinion,

Temp/mv is not a linear equation.

Same powder + different cartridge = different result.