Temperature Sensitivity Experience N560 and RL-26

Veteran

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I was recently down in Texas in 90 degree weather, and doing some shooting on our deer camp shooting range there.
I had loaded 5 powders to compare in my .338 Lapua Magnum.

N560
N565
RL-26
Retumbo
H1000

Previously I have had velocities for 84.9 gr N560 in the 2825-2850 range for 250 gr Lapua Scenar bullets with this rifle using Lapua Brass. It has a 26 inch barrel. The first 3 warm up rounds I shot, average 2916 fps from a cold barrel.......that shoulda been my first clue, something was up.

I shot some RL-26 rounds loaded with 90 and 90.1 Gr RL-26 using same 250 Gr Lapua Scenat bullets. They averaged 2979, and 2998 fps respectively.
I was expecting something more like 2870 out of these rounds based on QL and burn rate of .3397 for RL-26.

I had some 86.4 gr rounds N560 that then averaged 2931 fps, and then I shot 3 rounds of N560 at 86.9 gr that averaged 2944.
Based on previous work with these and modeling in QL I was expecting 2870 to 2885 fps at a burn rate of .3873

In reality, when I tried to figure out the actual burn rate for N560 it was in excess of .405 indicating temperature in the chamber had to be at least in
the 120-130 degree range. The RL-26 velocities were off the charts hot, and there was no way to make QL even go above 122 F to see what the actual burn rates were. They were certainly a lot hotter than .38 which is way hot for RL-26.

Since then, I have done some research on temperature sensitivity for these powders. It appears they were probably the most temperature sensitive of the powders (at least in high temps) I had loaded that day. I did not get to shoot any of the Retumbo, H1000, or N565 loads because I had a case head separation on the last N560 round that measured 2945 fps with 86.9 gr N560.

From what I have read, N560 is not as temperature insensitive as N565 and N570. It seems to have more sensitivity than the other V V's listed.
I read some horrible accounts of RL-26 at high temps with near max loads. It goes ape**** and bat**** at near max loads in hot weather.
It is supposed to be somewhat temperature insensitive, but over 90 degrees, that may be a myth based on my experience.

I see a lot of these temperature tests are run by freezing loads, and then testing them against room temperature loads. My take is this is no way to
state whether these powders are temperature insensitive. It covers only one tail of the distribution. Of course, I don't expect anyone to put their loads in a microwave and heat them up, but maybe taking them into 90 degree temps and shooting 15-20 rounds tells you something like it did me.

I think the Swiss, and the Fins, have no idea on the powders they manufacture what temperature sensitivity really is when they have never
experienced an August in Texas or Arizona. This is making me lean towards the Hodgdon's extreme powders or the Enduron Extreme powders for
shooting in really hot climates. If you have similar experience by all means contribute. Going from shooting in Michigan to Texas is a learning experience.
 

Rhett Crider

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Hornady's 4DOF calculator has a "temp sensitivity" box that you can plug in powders they've tested. Unfortunately, not much help on VV. Maybe Berger has tested since they are now part of NAMMO group. Worth a shot. As stated on VV website, N555, N565, and N568 are their temp stable powders. N560 and N570 are not.
 

Veteran

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Hornady's 4DOF calculator has a "temp sensitivity" box that you can plug in powders they've tested. Unfortunately, not much help on VV. Maybe Berger has tested since they are now part of NAMMO group. Worth a shot. As stated on VV website, N555, N565, and N568 are their temp stable powders. N560 and N570 are not.
OK, that helps explain the N560, and I guess I did not realize N570 was not temp. insensitive either.

But again, I just wonder what the Fins definition is of temp insensitive on the high end of the spectrum.

By the way I was down on the Pecos near Ft. Lancaster and Sheffield there in Texas.
 

Gstew1930

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I’m from south Texas. Ive noticed most powders aren’t very temp stable over 100 degrees. There are a few exception
 

highdrum

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No experience with N560, but I do in a few cartridges with RL26. These are smaller case capacities than you're using. My 6.5x284 load was developed in low 60° range and chrono'd at consistent 2980-2985. I shot it in late July in upper 90s and speed only increased to 2995. This is a pretty warm charge too, bout 0.7gr under ejector marks in cool weather. In the 90s I had shadow ejector marks but no bolt lift. All lots of a specific powder can have different temp sensitivities as well.
 

BrentM

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Meh. QL is a tool that is often not that accurate. I know some people swear by it, I have used and use it, but it's a model tool and nothing I ever hang my hat on.

I have run RL26 for 7 years and shoot from -10 to 90. I also run 560. Never have had an issue running upper node. I have had issues with ridiculously hot loads I developed in the winter tho. I run this powder in multpile cartridges and have burned through 5 kegs. I know people who run extremely hot loads have issues, duh. I have seen H4350 do bad things in 95 plus heat on a hot chamber and hot load. There is NO powder insensitive to temp. They all have a rating and ratings are based on generalizations. You have to approach this stuff considering the amount of powder you are burning and the weight of the bullet you are sending. You cannot just take .3 fps per degree and apply it to a 6 creed and a 300 RUM. That is why people put cartridges on a ice and in heat and use a heat gun to get an idea of the range of temp and fps per degree. It's a sound test, it works, and its been done this way for many years.
 

parshal

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I tested some 570 loads a couple years back from 13 to 75 degrees. Same load lot and those were air temps with the loads soaking for a couple hours. I found 570 to be less sensitive than R26.
 

highdrum

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I tested some 570 loads a couple years back from 13 to 75 degrees. Same load lot and those were air temps with the loads soaking for a couple hours. I found 570 to be less sensitive than R26.
570 is known to be one the most stable magnum powders.
 

Veteran

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There are more than one account of RL-26 out in the forums being sensitive at very high temps, at near max loads. The books show a max load of 90.6 gr for 250 gr Scenar in .338 Lapua. I was shooting 90 and 90.1 gr. So, I think these were not extremely hot loads, and I would bet in 70 degree temps they would actually compare closely to QL predicted 2885 fps. But, in very hot temps with a hot chamber they shot 2998 ish, almost 3000 fps for 250 gr. bullet. Like I said, this is very hottish behaviour for RL-26 in those charge weights. Had to be temperature related. The N560, I previously had lots of data for it shooting 2825 to 2850 at 84.9 gr. with 250 gr Scenar. It was shooting 2916 ish. Again, had to be temps. My experience on this says these powders can be a little volatile at high temps. I had shot maybe 15-20 rounds in 30 minutes. But your chamber does not cool very fast in these temps either.
 

Veteran

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One poster above says that Vihtavuori says N560 and N570 are not temperature insensitive but N565 and N568 are
according to their website. I commented, I had always thought N570 was supposed to be temperature stable too....so this was surprising. Does anyone have a link to temp. stability for all of the VV powders?
 

BrentM

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There are more than one account of RL-26 out in the forums being sensitive at very high temps, at near max loads. The books show a max load of 90.6 gr for 250 gr Scenar in .338 Lapua. I was shooting 90 and 90.1 gr. So, I think these were not extremely hot loads, and I would bet in 70 degree temps they would actually compare closely to QL predicted 2885 fps. But, in very hot temps with a hot chamber they shot 2998 ish, almost 3000 fps for 250 gr. bullet. Like I said, this is very hottish behaviour for RL-26 in those charge weights. Had to be temperature related. The N560, I previously had lots of data for it shooting 2825 to 2850 at 84.9 gr. with 250 gr Scenar. It was shooting 2916 ish. Again, had to be temps. My experience on this says these powders can be a little volatile at high temps. I had shot maybe 15-20 rounds in 30 minutes. But your chamber does not cool very fast in these temps either.
So book data is also a reference. They test those loads in a test barrel with xyz components. Unless you are shooting the exact same everything that is just a guide. I rarely get over book max because I run lapau, adg, peterson, etc brass. Those books use remington, winchester, hornady etc. IMHO I only use book data to get a starting reference point to conduct a velocity ladder test and ident pressure at what that particular set up is going to handle.

Most data I see on FPS/degree shows .3 for those powders. I have found it to be less in a creeds, 6.5-284, and PRC but it's a starting point I suppose.
 

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