Temperature Sensitivity Test: IMR 8133 and Reloder 26

entoptics

Well-Known Member
Joined
Jan 16, 2018
Messages
618
Just ran a fairly rigorous temperature sensitivity test on IMR 8133 and Reloder 26 in my 7mm RM.

Equipment.

26" X-Caliber prefit, 1:8 twist, fluted heavy sporter.
Sartorius high precision scale for powder charges ( ≤ 0.03 gr ES for charge weights)
LabRadar
Indoor/Outdoor thermometer set (crappy, but within a couple degrees of 2 other crappy thermometers)
175 ELD-X, RL26 and IMR8133, Fed 215M primers, R-P brass, 3.335 OAL (~0.020 off lands).

Method.

1) All rounds were loaded in one session, using my standard methods. Neck turned, ~4X fired, annealed every firing, FL sized (shoulder bump 0.002"), sinclair neck mandrel expanded, and trimmed. Pin tumbled, graphite lube in neck.

2) An aliquot of 5 rounds was placed in a cooler with ice (~32° F) for transport, and a second aliquot was placed in another cooler with 3 Nalgene bottles full of boiling water. Since it was a steady 29º F for the shooting session, the "Cold" aliquot was taken out of the cooler, and left outside on the ground next to my shooting position, with a thermometer in the lid of the ammo box. Both aliquots had ample time to come to a near equilibrium temperature (>2 hours), though the "Hot" rounds obviously slowly cooled during transport and setup from ~135° F initial temp, to ~100° F when fired.

3) Rounds were fired in 4 shot strings, 2 "Cold", then 2 "Hot" (to ensure maximum chamber heat for the "Hot" aliquot). The barrel was then allowed to cool to ambient temp before the next 2x"Cold" and 2x"Hot" string of 4. The last two rounds were fired 1x"Cold" and 1x"Hot", for a total of 5 shots of each temperature.

4) Both sets of loads were on the toasty side for this rifle (I was exploring top end loads for these powders), and based on the velocities, are probably at or slightly above SAAMI max.

Results.

Reloder 26 - "Cold" average = 3010 fps, "Hot" average = 3015 fps. ~0.1 fps/deg
Screen Shot 2020-12-29 at 8.39.58 PM.png


IMR 8133 - "Cold" average = 3060 fps, "Hot" average = 2989 fps, -1 fps/deg (dubya tee eff!?!?!)
Screen Shot 2020-12-29 at 8.44.42 PM.png


Discussion.

Reloder 26 performed admirably, with an ES of 21 fps and SD of 8 fps across all shots.

IMR 8133...I don't know W.T.F. is going on here, and can think of no explanation. ES/SD was rather high for each aliquot, but well outside error. I've replayed the shooting in my head over and over, and I'm 99.9% certain there's no way I reversed the shot order, as I intentionally shot the "easy to grab" cold rounds out of the box at my elbow first, then shot the ones I had to dig out from under a wool shirt and inside the cooler, 2nd. I know for a fact that the last two were 1x"Cold" then 1x"Hot", as I pulled some hot water out to give to my dogs since the experiment was finished, and those two also showed the extreme difference (Cold 3078 fps, Hot 3000 fps). As also mentioned, I loaded these in the same sitting, and they were only separated into aliquots this morning when I put them in their respective coolers.

The results for IMR8133 are so odd, that I think it requires a retest before putting much stock in the outcome. I will hopefully get a chance in a week or two when the grubby weather that's inbound has passed. I'll probably use my 264WM for that, to get another data point.
 
Last edited:

P7M13

Well-Known Member
LRH Team Member
Joined
Jan 5, 2016
Messages
814
Location
Orygun
Thanks for your research.
Lot of info on 8133 lately. I passed it up and purchased 7977 instead because it was (supposedly) closer to H1000 and RL26 in performance.
Alas, still stuck in a time warp with no freedom to get to my reloading bench.
 

MallardAddict

Well-Known Member
Joined
Feb 10, 2005
Messages
658
Location
Rainy Western Washington
I’ve never had much issue with r26 loads that I developed in the summer being much slower when shot colder. I have had pressure issues in both my 7SS and my old 6/5 saum on loads developed and shot at 35 degrees ambient getting high pressure when shot above 80 degrees
 

Idaho Trecker

Well-Known Member
Joined
Apr 19, 2013
Messages
1,013
Location
North Idaho
I've had great luck with 26 for my testing also. I dont have my notes handy as to the temps I tested at but I came up with .2fps/degree swing.
I also did some testing with 8133 with temps at 10, 35, and 70 degrees. I came up with basically the same funky results with big ES and the average of each set equating to .7fps/degree swing. I've also loaded for a friends 338 rum with 8133 and had great speed and accuracy. The next time shooting the same load the accuracy was gone and speeds all over the place. It's amazing how I've read a lot of people having bad luck with 8133 but it's supposed to just be the imr version of retumbo with copper fouling reduction.
 

Dosh

Well-Known Member
Joined
Aug 6, 2013
Messages
3,867
Location
Arizona
Not surprised with the 8133 result. Tested it in my 30/378 Wby @ 90 degrees with bizarre pressures at medium Hodgdon published charge. It actually had hard bolt lift. The remainder of the pound is sitting way in the back of the cabinet. Tried it when I was low on Retumbo, I've since acquired a good supply.
 

Rhovee

Well-Known Member
Joined
Jun 29, 2017
Messages
1,272
Seems like you need to test temp stability of powders for each gun. I did a test with 26 in my 300 wsm and lost .75 FPS per degree. I froze ammo in a hydro flask for 3 days. Shot them next to ammo in 70 degree weather and tested. The ES was consistent, 12 FPS, but it was 2960 compared to 2930
 

eshorebwhntr

Well-Known Member
Joined
Apr 11, 2009
Messages
606
Location
MD
I’ve never had much issue with r26 loads that I developed in the summer being much slower when shot colder. I have had pressure issues in both my 7SS and my old 6/5 saum on loads developed and shot at 35 degrees ambient getting high pressure when shot above 80 degrees
Just about exactly what I saw with R26 in a 6.5x284 Norma
 

BallisticsGuy

Well-Known Member
Joined
May 8, 2016
Messages
1,181
Location
Heck
Exactly what I've come to expect of the new IMR powders. Fantastic temp stability and the spreads within temperature regions are nice and stable. Nothing like as erratic as some others. RL23 might be worth a look too. From the limited data I have for RL26, it looks like it goes bonkers after 90F which a lot of powders that are otherwise known for being pretty stable do too. Kinda curious to see below zero numbers. I'll bet things get lumpy down there for RL-26 too.
 

entoptics

Well-Known Member
Joined
Jan 16, 2018
Messages
618
It does no good to test cold ammo in a hot gun. Only way to do it right is to shoot both gun and ammo at ambient temp.

When winter testing, I leave both gun and ammo in the unheated garage to cold soak over night.

You might have missed it in the "Methods" section, but I did exactly that. Cold rounds were fired in cold gun (2 shots), then 2 shots of hot rounds immediately after. Cooled the gun to ambient temp with a blower, rinse, repeat.
At excessive pressures velocity can start to drop.
I thought about this. Not a bad point, and the "velocity plateau" you sometimes see near max pressure, could also explain the lack of sensitivity in the RL26 test.

So what have we learned? If you're afraid of temperature sensitivity, just run that puppy well over max PSI and you're good to go! 🤪
 

Recent Posts

Top