Temperature Sensitivity of Alliant Reloder 26

[codyadams]

If you are part of the "Reloder 26" thread you have already seen this, but I felt it was somewhat useful and could use it's own thread. I have seen other people make threads on this subject, but nearly every one I have seen, the tests were conducted on different days, which can inherently induce some inconsistencies, and may not be a fair test. I am not by any means saying that the test I conducted was without flaws, I just feel that it may take out some of the possible variables. And I do plan on repeating this test in the future to check for consistency.

So here is how I conducted my test. I put 5 rounds in a zip lock bag in my freezer overnight, then on my way to the range I put the rounds in a bucket filled with ice, and put my kestrel inside so I had a temperature I could monitor and record. The other rounds were kept at room temperature in my house, then on my dashboard in my truck on the way to the range.

When I got to the range and set up my chronograph, I got my bucket of ice and pulled my kestrel out and looked at the temp, it registered 17° f, but by the time I thought to get my phone out and take a picture, it had warmed up to the 37, as the ambient temp outside was in the high 60's. After this I put my kestrel in my ammo box with my room temp rounds, so it could stabilize and tell me the temperature of those rounds while I fired the other ones.

First I shot the chilled rounds, pulling them out of the ice one at a time, and I shot them within about 3 seconds of chambering them, and recording velocity. Then after that, I let my barrel cool to room temp, then looked at the temp in my ammo box, which was 67 ° f. Then I shot those 5 rounds, and recorded velocity.

This was my load for all rounds fired in my .260 AI:

49.1 grains RL-26
Lapua Brass
CCI BR-2 primer
140 Berger VLD Seated .005 off lands

And these were my velocity results:

17° f -
1. 3051
2. 3046
3. 3056
4. 3066
5. 3055 AVG. 3054, E.S. 20 FPS

67° f -
1. 3060
2. 3059
3. 3055
4. 3058
5. 3063 AVG. 3059, E.S. 8 FPS

My lower temp loads would have had a 10 fps e.s. If it wasn't for the one that went 3066, and also would have averaged 3052 instead of 3054. But even at that...The velocity spread for 50° f difference was only 7 fps...so all my worries about temp sensitivity are now dismissed, at least for this rifle.

I will point out that I did use an optical chronograph, as I do not have anything better at this time. But I feel that the fact that these rounds were fired within 20 minutes of eachother, on the same EXACT day, with the same EXACT lighting, the same EXACT distance to the chrono, the same EXACT shooting positions, and the chrono remained turned on the entire time, that it shows a distinct point. If these were changing 1 fps per degree, with a 50 degree change it certainly would have shown up on even an optical chronograph. With my test, it showed a change of .14 fps per degree. And I know this velocity to be correct, As I have verified this by the use of applied ballistics mobile out to 1100 yards.

I hope some will find this useful, and when I conduct any further temperature testing, I will add it to this thread.

 

[Rich Coyle]

Thanks for the good info.

 

[RevJim]

Thanks for the test! I really like R26, in some cartridges I have yet to get the accuracy I was quickly looking for, not saying I couldn't have tested seating depth more. I think a powder's temp sensitivity depends on the size of the case. For example, R19 gave me almost a 200fps drop ( was checking my zero for a late season cow elk hunt, was shooting "patterns" so ran them over a chrono.) in a 338 WinMag/185 XLC load that had been worked up in 90 deg,one cold December at 10 degrees. I pulled the bullets and the powder (barely a compressed load) had to be dug out w/screwdriver! A fast workup in one day with H4350 saved my hunt. In two .240 Weatherbies/90X,TXS,etc R19 is stable as a rock! So testing, as you have done saves time later for those who can do it. But it always pays to check velocity ( zero for sure) when the temp drops. Most people ( and rightfully so) pay more attention to hot days than cold days.
I have a friend in South Africa who was using a known load in his .308 (180 MagTip) and Somchem Powder (sp?) on a cull Eland hunt in the Draknor (again, sp?) mountains around zero degrees. The bullet barely got through the hide! He finally made a headshot that "barely" got into the brain, this was all done at under 100yds too. He was bumfuzzled, but learned a good lesson. He fortunately had a backup rifle, another 308 but using Military fmj ammo for headshots. He was a former soldier who used an R1 (FN FAL South African copy) for over a dozen years so he knew it would work at cold temps. It pays to check ones ammo at severe temp swings for sure.

 

[Laelkhunter]

Has me thinking that I should try a similar test with the RL19 reloads for my .340 Weatherby. I don't have a Kestrel, but should be able to find a thermometer.

 

[Barrelnut]

Try a laser infrared thermometer. I used one when I did some of this testing. You can take an instant temp right off the brass before you chamber it. Got mine at Harbor Freight.

https://www.amazon.com/dp/B00DMI632...t=&hvlocphy=9032960&hvtargid=pla-309607628772

 

[Dgd6mm]

Good information, thanks Cody.

 

[Rich Coyle]

Try a laser infrared thermometer. I used one when I did some of this testing. You can take an instant temp right off the brass before you chamber it. Got mine at Harbor Freight.

https://www.amazon.com/dp/B00DMI632...t=&hvlocphy=9032960&hvtargid=pla-309607628772

I use a different one, but it works like yours. When I hit the button it gives me ambient. Hit it again and get the temp of whatever it is aimed at. The ammo is left in the pickup overnight so it is ambient. The trouble with the ambient is the temps here in Grants Pass, Oregon are going up.

I use it for barrel temp also.

 

[FURMAN]

Very good information Cody. I have seen at least one other test on the internet. It seems to be a stable powder. Too Bad R33 was not getting the same results.

 

[JJMoody]

Bump. Looking for a bit more info.

 

[dok7mm]

Thank you Cody, very informative test. I wonder what a test at higher ambient temperature would show. Say 60* to high 90* and how that would impact at 20-40* hunting temperatures. I ask because I shot pressure tests at 75-80 degrees in a 6.5 Sherman with RL-26 vs Retumbo. I got definite pressure @ 3,100 fps with RL-26 and 3,150 fps and no pressure w/Retumbo. Expected exactly the reverse, based on other's experience.

 

[Bullet bumper]

Thank you Cody, very informative test. I wonder what a test at higher ambient temperature would show. Say 60* to high 90* and how that would impact at 20-40* hunting temperatures. I ask because I shot pressure tests at 75-80 degrees in a 6.5 Sherman with RL-26 vs Retumbo. I got definite pressure @ 3,100 fps with RL-26 and 3,150 fps and no pressure w/Retumbo. Expected exactly the reverse, based on other's experience.

That is because other people LIE to sell their product over another .
Retumbo is made in Australia by ADI and is specially made to be less heat sensitive .
Reloader powders are less sensitive than Ball Powders but not as good as the ADI made Hogdon line .

 

[Wedgy]

Thank you Cody, very informative test. I wonder what a test at higher ambient temperature would show. Say 60* to high 90* and how that would impact at 20-40* hunting temperatures. I ask because I shot pressure tests at 75-80 degrees in a 6.5 Sherman with RL-26 vs Retumbo. I got definite pressure @ 3,100 fps with RL-26 and 3,150 fps and no pressure w/Retumbo. Expected exactly the reverse, based on other's experience.

I live out west where it gets hot in the summer when we pig hunt because nothing else is open, and I do testing also. The other week I got to test loads with a big temp swing to the "hot" levels. Speeds were with Labradar
Load is 7mm RUM 143 grain Hammer HBN 93.0 Reloader 26 CCI250 3.6"
On the 12th it was 68F and speeds were 3601, 3604, 3606, 3610
On the 16th it was 95F and speeds were 3649, 3650, 3651, 3655

So more or less a 27F rise gave about~ 50fps gain in velocity at the temp swing from 68 to 95F. That's 95F in the shade and yes I had the range all to myself. The rise puts this load to where primers really flatter and faint ejector marks. It boosts it a little over what a grain of powder increase would yield. I have a 6.5x284 load with IMR7828 that I cannot shoot in the hot temps (above 85F) as it sees a huge increase. A lower charge isn't accurate enough to keep.
So the term "temp stable" is within a range that most hunt but I think somewhere around the ~83F mark the fps per degree really starts to increase.
I know Shawn of Defensive Edge uses H1000 because he said it was the most stable powder he tested even though he got more velocity from others.

 

[dok7mm]

I live out west where it gets hot in the summer when we pig hunt because nothing else is open, and I do testing also. The other week I got to test loads with a big temp swing to the "hot" levels. Speeds were with Labradar
Load is 7mm RUM 143 grain Hammer HBN 93.0 Reloader 26 CCI250 3.6"
On the 12th it was 68F and speeds were 3601, 3604, 3606, 3610
On the 16th it was 95F and speeds were 3649, 3650, 3651, 3655

So more or less a 27F rise gave about~ 50fps gain in velocity at the temp swing from 68 to 95F. That's 95F in the shade and yes I had the range all to myself. The rise puts this load to where primers really flatter and faint ejector marks. It boosts it a little over what a grain of powder increase would yield. I have a 6.5x284 load with IMR7828 that I cannot shoot in the hot temps (above 85F) as it sees a huge increase. A lower charge isn't accurate enough to keep.
So the term "temp stable" is within a range that most hunt but I think somewhere around the ~83F mark the fps per degree really starts to increase.
I know Shawn of Defensive Edge uses H1000 because he said it was the most stable powder he tested even though he got more velocity from others.

Thanks Wedgy, that's exactly what I'm dealing with for summer shooting. I have come to believe that temperature/ velocity relationship is much more stable in low to moderate temperature conditions, but can not be relied on for upper range temperatures, where it tends to spike. Of course, there are other variables such as ambient temperature of ammo and time for barrel/chamber to return to ambient temp. I'm sure that loads worked up to highest accuracy nodes are more susceptible to pressure spikes in the heat. For now, I'm more inclined to stay with Retumbo & H-1000 and wait for cooler weather to confirm my long range drops.

 

[Wedgy]

Thanks Wedgy, that's exactly what I'm dealing with for summer shooting. I'm sure that loads worked up to highest accuracy nodes are more susceptible to pressure spikes in the heat. For now, I'm more inclined to stay with Retumbo & H-1000 and wait for cooler weather to confirm my long range drops.

I do enough hot weather shooting that I need a hot weather load. Two years ago it was 87F on a Wyoming elk hunt at 7,000' in late October, not the norm but it happened so we need to be prepared. I thought the Sig Kilo 2400 AB has some function for powder temp/speed adjustment but I've been too busy to take it out of the box let alone read the instructions. I have Andy's video to watch haven't gotten around to watching it.
As far as barrel temp goes I use a rechargeable air mattress pump with a variable speed control to cool the barrel off as it takes forever when it's this hot. All ammo is at ambient temp and I'm out there for half the day plinking with other rifles while things cool.
I will probably drop this load down to ~92.0 grains so I'm not over max when it's hot then go from there. Or have a hot and cold weather gun. Or i guess I could just have two different load profiles for the Kilo 2400 if they are that different. Perhaps somebody who is in the Kilo know can comment.