n570 temperature stability

slowshot18

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I'll be heading to Colorado for 3rd rifle in November. Currently, I live in Texas. Huge difference between temperatures in Texas and at 10,000'+ in Colorado this time of year.
My load development for my 28 nosler has been performed in TX, average temps in the 90's. Velocities recorded using a LabRadar.
Last weekend we enjoyed a cool spell and I had the opportunity to shoot in 65 degree weather. I noticed a velocity drop of 10 fps with the same charge as what was worked up in the low 90s. I expected a slight change, but not this big of one.
Also, I've read that fps loss is not linear with temp drops. Where I will be going to hunt I could encounter temps in the teens or lower.

Does anyone have any real world experience/data as what I could expect? Just trying to prepare for what my limit on max distance shot will be. Before this discovery, I was comfortable with 700+ yards contingent upon wind, but now, if velocity loss is going to be drastic, I might limit it to 400 yards.
Note: I use a kestrel elite for my shooting solutions.
 

slowshot18

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Take yer Lab with you and do some shooting when you get there. Early morning when its cold before you start yer hunt might be best way to tell. Change the velocity in yer Kestrel.
That was going to be my backup plan! I was just trying to avoid one less thing to drag out there.
 

Shane Lindsey

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Interested to see your results. I use N570 quite a bit. I would think you were at the extreme side with 90 degrees.

Hopefully less shift from 65 and below. Have you put any in the freezer overnight and then shot over the chrono. Not the same, but a little closer. May give you an idea. We used to use a 20 degree shift up or down was a minute to the elevation.

Considering you are going higher anyway, I would check zero and velocity as stated above once you get there if able.
 

slowshot18

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Take an ice chest and put your ammo on ice. Go to the range, pull the ammo out 1 round at a time and shoot it over the LR before you go. That should get you the data you need.
I’ll give this a try this weekend and see how it goes!
Interested to see your results. I use N570 quite a bit. I would think you were at the extreme side with 90 degrees.

Hopefully less shift from 65 and below. Have you put any in the freezer overnight and then shot over the chrono. Not the same, but a little closer. May give you an idea. We used to use a 20 degree shift up or down was a minute to the elevation.

Considering you are going higher anyway, I would check zero and velocity as stated above once you get there if able.
Thank you! I’m going to try the cooler method on the way to the range after they’ve been in the freezer before I leave.
n570 is very stable
Rich, do you see a drastic difference in velocity from working up a load in the summer and then trying it out in the winter?
 

jrock

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Wow, 10 fps drop from 90 to 65! That's pretty stable. I have some second hand data on N565 being <0.4 fps/deg, which is pretty good. I also recommend putting 3 rounds in the fridge and 3 in the freezer. Then packing a cooler with ice packs to take it to the range. I put a thermometer in the cooler and then use an inferred thermometer to measure the case temps prior to chambering. You need to shoot them rapidly before the chamber heats up. Don't let the round dwell in the chamber. Chamber and shoot. They can absorb chamber heat if you let them sit too long. Also, shoot three ambient temp rounds in the same outing after the barrel has cooled. Those three data points will give you a good rate of change to use in your ballistics app.
 

jwing

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So the ammo in ice thing is not true. Metal contracs in the cold.
You have to have the gun and ammo in cold to get the true difference.
And n 570 is very temp stable .
 

jrock

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So the ammo in ice thing is not true. Metal contracs in the cold.
You have to have the gun and ammo in cold to get the true difference.
True, one would be better off to avoid artificial temperature changes. Hence, my emphasis on zero dwell time in the chamber. A chamber chiller would be a good tool to use as well.
In a pinch, the cooler method has given me acceptable data, YMMV. It will tell you what ball part sensitivity you are dealing with. Whether its 1fps/deg or 0.5fps/deg.
Best of luck
 

Veteran

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Here's a link you may find helpful. In this link someone said that according to Vihtavuori's website, only N565 and N568 were claimed to be temperature insensitive. I don't know that for sure, its just what was said in another thread.


Out of curiosity though I did some modeling in Quickload. I took my .338 LM data files for N560, N565, N568, and N570.

I varied the temperature by 30 degrees from 70 to 100 leaving all other inputs constant for each powder.

What I saw was a variance of about 1.23 to 1.66 FPS in velocity for each degree of temp. change for these powders.

N565 was the least sensitive only varying 1.23 FPS per degree. N568 and N570 were the most sensitive varying 1.63 to 1.66 FPS per degree. I note they are the lowest burn rates of these powders, and the way that Quickload handles the change in temperature is to modify the burn rate according to some correlation it has internally. So, the lowest burn rates were the most sensitive per degree of temp. change. Seems a little counterintuitive, but the N568 is a more fine grained cut, and the density may have some bearing, and the chemistry of these powders may also have some bearing.

If you are getting only 10 FPS change for 30-35 degrees change, you are doing better than expected IMHO.

It could be more like 30-50 FPS and at higher altitude, you can expect it to be that much or more just due to the difference in
air density out to range, (not at the muzzle, but over 300-1000 yards). Run some ballistics projections at your altitude with your sight in zero, and run them again at 10,000 feet with difference in station pressure, and altitude. See what the differences are in
velocity at distance. Its going to be more than you expect. Both due to temperature, and air density. That's why folks sighting in
on the Texas Gulf Coast at sea level end up shooting way over the backs of their elk up in the mountains.

Best to sight in and check everything on site before the hunt!

By the way, none of these powders are totally insensitive to temp. Not Retumbo, Not H1000, Not RL-26. They all can act bizzaro
under 95 degrees plus temp when you develop a hot load at 70 degree temp and take it into really hot weather, especially in a heated chamber or barrel.
 

Mike Matteson

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You can be looking 20 below at time there in Colo. That doesn't include chill factor either. You loose about 1* per mile per hour of wind speed. Temp might get up to 50* in the day. Be able to dress up or down depending how the weather is during the day. Be able to layer up or down. Will need a day pack to do that. Besure you have cool weather boots, if they have liner in them, have a second set to allow for one set to dry, and change out daily. I hunted several 3rd season there from the 7-10,000 ft range. Now I hunt within a group, but on my own mostly each day. The other be sure you a -20 sleeping bag. I can add to that, but not knowing what your camp site is going to be. If you have any question, please feel free to ask.
WISH YOU THE BEST OF LUCK!
 
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