About a year and a half ago, I retired and moved from SE Alaska to Alabama. Temps I was shooting in ranged from 25~ to 65~. Heat was not an issue, nor were significant temperature swings. Although I read a little about temperature sensitive powders, I really don't understand the specific impacts of temperature fluctuations or how much of a fluctuation is required to see changes in performance or safety. Now that we're back in the southland, I thought I'd pose a question or two. I'm hoping some folks with real world experience will share some thoughts and experiences. CFE seems to be the most popular powder mentioned when discussing temperature sensitivity and I have a few loads with CFE that do pretty well for me.
How high does the temperature have to hit before you see changes? Is there an actual top end, or is the issue more of a significant change in temperature? Are there other environmental considerations, such as humidity, that also need to be considered from a pressure / safety standpoint? How do you monitor changes? Is it all trial and error while tracking environmental conditions and load performance? What else should be considered?
I can say, I won't likely be in any 100 plus degree temps shooting, but I may be out in the 90's. We may bump into some humidity as well. Any thoughts or wisdom would be greatly appreciated.
Temperature sensitivity has to do with variations of muzzle velocity (MV) (what you can see) and the underlying variations in peak chamber pressure (which you can't see) as temperature goes up or down. There are a couple of publicly available tables that show values of how many ft/s per deg F, of MV you get from a powder for a higher/lower temperature. The PRS blog, IIRC, also did a couple of studies on Varget, H4350, and IMR4166 as to temp sensitivity of those.
CFE in the one table I have, is said to have a variation of 1.7 ft/s/degF, whereas Varget is in the 0.2's (H4350 also).
The variation, even in those studies, is not completely linear but mostly so. It tends to accelerate at higher temps and slows down a bit at lower temps.
The temperature of the cartridge/powder when you fire it is the main component, b/c at a higher powder/internal temp the powder can burn faster... chemical reaction and all.
Now, I did a small comparison of my own, of some RL-17 in my 6.5 CM, b/c I have some and it does nicely in my CM. RL-17 has a 1.42 ft/s/deg value in the table-- my comparison came up with 1.0. This was over a range 70-43 deg.
One other caveat, and this is my own theory: the amount of delta you see for temp change could be related not only to the powder but also to the case size and burn efficiency of the cartridge. What might be 1.7 in a 223 or 308 (whichever) might be more or less in a 6.5 Grendel. I suspect most studies were done with 308 ammo; I haven't seen any studies that showed how a particular MV change might vary in a different cartridge or in a more/less efficient cartridge.
So. For CFE my approach is, since most of my shooting is done in an indoor range my baseline is 70 deg... I don't normally go out into temps above say 85, nor do I do much sub-freezing shooting, so for most cases CFE does well for me. I probably wouldn't take it with me for >100 yd shots at 30 deg (hunting in Va in Nov-Dec)... but for general shooting - no problem as far as I'm concerned.
"Down the floor, out the door, Go Brandon Go!!!!!"
kpswihart Wrote:About a year and a half ago, I retired and moved from SE Alaska to Alabama. Temps I was shooting in ranged from 25~ to 65~. Heat was not an issue, nor were significant temperature swings. Although I read a little about temperature sensitive powders, I really don't understand the specific impacts of temperature fluctuations or how much of a fluctuation is required to see changes in performance or safety. Now that we're back in the southland, I thought I'd pose a question or two. I'm hoping some folks with real world experience will share some thoughts and experiences. CFE seems to be the most popular powder mentioned when discussing temperature sensitivity and I have a few loads with CFE that do pretty well for me.
How high does the temperature have to hit before you see changes? Is there an actual top end, or is the issue more of a significant change in temperature? Are there other environmental considerations, such as humidity, that also need to be considered from a pressure / safety standpoint? How do you monitor changes? Is it all trial and error while tracking environmental conditions and load performance? What else should be considered?
I can say, I won't likely be in any 100 plus degree temps shooting, but I may be out in the 90's. We may bump into some humidity as well. Any thoughts or wisdom would be greatly appreciated.
I want to add one more thing. If the node you're in (MV-wise) is broad, then POI in general may not be affected much by a drop in velocity, under 200 yds. Example: suppose the node is 2480-2515... if you are at a normal MV of 2510, then 20-30 deg drop in temp may put you down to 2480 or so, so relatively speaking, accuracy and POI might still be pretty much as the original. This is not an exact science however...
IMO most of the temp-related concerns are relative to extreme temp swings, or to long distances, >500 yds...
Stay safe.
"Down the floor, out the door, Go Brandon Go!!!!!"
Caleb Wrote:Is there a cfe 223 substitute that hits the velocities cfe hits in cases that is more temp stable and semi easy to meter
For me that would be h4895. I'm useing it in my bolt action grendel.
Haven't tryed it in the ar grendel yet. Ar-comp seems to get me very close to are matching what cfe223 would do speed wise from my ar grendels but is much more temp stable compared to cfe223.
Basically most all ball powders are more temp sensitive than extruded stick powders. Most of the Hodgdon extruded stick powders are much less temp sensitive like H4895 as mentioned. The IMR Enduron powders are supposed to be temp stable but I have not used any. IMR 8208 is also a very temp stable powder and is what I use in my 6.5 Grendel 120 gr bullet loads. I have not worked much with lighter bullets. I did quite a bit of work trying to get the 123 Hornady SST to shoot but neither of my rifles liked that bullet no matter what powder or charge I tried.
For my uses and temp stability, I'm using the AR comp and the 8208XBR. Xbr for 90-110 and ARC for the 120 class, like 120 gold dot, 123 sst and 123 eldm. Those are the bullets I use.
I tried ARC with the 120 pro hunter and one try it seemed pretty good, but the gold dot and 123's have better BC's so I don't use that PH in my grendels... at least not now.
Some guys use Xbr successfully for the 120 class, but do be careful b/c that powder can spike on you quickly as you get to the top end of the powder range.
Haven't tried H4895 yet, but I use that in couple of other calibers and like it there.
"Down the floor, out the door, Go Brandon Go!!!!!"
"Your FAT! No good useless and ugly! Can't hit the broad side of a barn!"
Tested my Reloader 15 after yelling the above at it and yup it was sensitive!
If you do load development when it's hot, it's safe when it's hot. When it's cold you could put the ammo/magazine in a warm place like a pocket with a handwarmer.
I've been thinking of starting a thread on ways to mitigate sensitivity. Chime in if you have some nifty ideas!
I have found that if working with near max charges, temperature sensitive powders are more likely to have issues. The least sensitive powder that seems to work in my .458x1.8 while still providing a usable velocity with a Speer 400gr is IMR 4227. This seems to be around 1.17 on sensitivity charts. I do see minor changes in how the cartridge performs between spring/fall and summer weather. IMR 4227 does seem to have the benefit of probably not being able to get enough in the case to be a real concern. If I use W296 I have to find my max load during summer. If I develop the load in spring or fall it will be borderline unsafe in the summer. Its a little concerning when you start to flatten out the head stamp on a belted case.
Living in a relatively hot environment I learned years ago to work up max loads in the Summer not the Winter. I have had great shooting loads in the winter that were over pressure in the Summer when there might be a 70 degree temp swing.
When using a public range in Texas I got to where I would do all my load workup June to August, often had the range to myself or nearly so.
Generally speaking single base powders are more temp stable than double base powders.
In my limited experience, temp sensitivity isn't really an issue unless you're messing with maximum loads.
Also, don't let cartridges sit in a hot chamber for an extended period, or in the hot sun or vehicle, before firing. These extreme high temps with cause a far greater swing in velocities and pressures than ambient temperatures will.
Great info. Anyone have any specific load data with measured or observed effects to share? I would be interested in reading about actual changes folks have experienced.
03-19-2020, 01:27 PM (This post was last modified: 03-19-2020, 01:31 PM by Grendelshooter.)
kpswihart Wrote:Great info. Anyone have any specific load data with measured or observed effects to share? I would be interested in reading about actual changes folks have experienced.
Its been a long time, a few years anyway, since I played with 2520 in 5.56.
Behind a 77gr SMK (trying to duplicate mk 262) it varied by more than 100fps over a 40 to 50 degree temperature range. Charges were -10% book max to .5gr over book max. I think the highest temp I recorded data at was 97*f, low was in the 40s. Iirc low temp velocity was in the 2680s, high temp over 2800 (2806 sticks in my mind). This out of a Douglas SPR barrel from CLE with the CLE match 5.56 chamber. Book max from Alliant was pretty gnarly during the summer, brass was done (primer pockets loose) after 2 firings. Velocity measured by a magnetospeed.
After that I moved to TAC and then 8208 in load development. Neither was consistent for me though of the three mentioned TAC was the best. It still swung pretty wildly with temp but I think it was right around 1fps/deg f. 8208 just never got me accuracy or speed, I threw a half pound of it away in frustration.
Then I found AR Comp. 23.4gr behind a 77gr Nosler CC or Hornady 75bthp in a Wylde chamber makes consistently small groups with great velocity and no real great temp instability...in my rifle anyway.
kpswihart Wrote:Great info. Anyone have any specific load data with measured or observed effects to share? I would be interested in reading about actual changes folks have experienced.
107 TMK
30.6gr A2520
CCI 450
2.26"
I only shoot it under 80 degrees so take it for what it's worth. If you're shooting in big temperature swings record your data and load for the different velocities. My load changes about 40 degrees from 30 to 80 degrees ambient.
Klem Wrote:Single-based powders are more temp stable than double-based.
Hodgdon buys a lot of their power from ADI. The ADI factory only makes single-based. You lose a bit of energy density but it's more temp stable.
I'm using 8208 because I think I want temp stability and supply is good and reliable down here (as ADI BR8208).
It does seem to fill the case and I've wondered if there is a denser powder.
I'm not sure which is more important: stability, density or spikiness.
Perhaps solve all three by going to a smaller load of 8208 ...
