Question on Temperature Sensitivity

[rayatphonix]

I read a lot about some powders being temperature sensitive, and in fact use several powders that are considered as such. My question is at what temperature range does that become a factor? Where I live and hunt temperatures generally range from the 40's to mid-80's, at least when I shoot. Occasionally it'll reach 30 degrees during hunting season. Consequently I don't worry about it. My loads are developed for accuracy and I don't recall anything I load being at or near the max safe load. Am I making a mistake?

 

[Wreck-n-Crew]

Admittedly I am at a loss to provide anything of use to your question but I would say that listing the powder you use might aid in getting a better answer for your specific needs. As much as the subject comes up I still have only reading experience. I'll be watching this one because I myself would like to hear what some of these guys with more experience and testing have to say Good luck!

 

[rayatphonix]

I use RL-15 and RL-17 for several rifle and bullet combinations. For instance 6.5 Creedmoor, 140 gun bullets and RL-17 work well for me. The latest powder, RL-16 isn't supposed to be temperature sensitive.

I use RL-15 on a couple of others.

I work up most loads in the summer, and hunt in the fall and winter.

 

[LiveLife]

W231/HP-38 is temperature sensitive which means your loads will chrono faster on warmer days. Due to this reason, many match shooters needing to meet 125 power factor will use higher powder charges in winter or simply load to higher 130 PF. It is also why many match shooters use Titegroup, which is less temperature sensitive than W231/HP-38, with less/no need to adjust powder charge to meet PF.

Here are chrono number difference between 56F and 79F:

115 gr RMR HM RN 4.8 gr W231/HP-38 @ 1.130": 1275-1263-1253-1290-1248 fps (56 F - JR carbine)

115 gr RMR HM RN 4.8 gr W231/HP-38 @ 1.130": 1303-1289-1298-1311-1323 fps (79 F - JR carbine)


WSF is reverse temperature sensitive which means your loads will chrono slower on warmer days. I am finding that Promo may be reverse temperature sensitive - https://www.thehighroad.org/index.php?threads/is-promo-reverse-temperature-sensitive.808919/

100 gr RMR HM RN 4.5-4.7 gr Promo @ 1.050": 1478-1475-1480-1471-1467 fps (58 F - JR carbine)

100 gr RMR HM RN 4.5-4.7 gr Promo @ 1.050": 1458-1450-1445-1442-1448 fps (71 F - JR carbine)

Many more loads tested with specified ambient temperature - https://www.thehighroad.org/index.p...n-9mm-40s-w-45acp.799231/page-4#post-10338994


Here's a listing of temperature sensitivity of powders - https://www.thehighroad.org/index.p...s-and-discussions.778197/page-7#post-10117881

Standard/Temperature sensitive powders (produces higher velocities at higher temps):
- Clays
- Titegroup
- W231/HP-38
- Power Pistol

Reverse/inverse temperature sensitive powders (produces higher velocities at lower temps):
- Competition
- WST
- Promo (Doing more testing to verify)
- Solo 1000
- N320 (but some claim normal temp sensitivity)
- SR7625
- Universal
- WSF
- Silhouette

 

[kingmt]

Where I live and hunt temperatures generally range from the 40's to mid-80's, at least when I shoot. Occasionally it'll reach 30 degrees during hunting season.

Where do you live? I may want to move there.

I can't help much with your question but have read of people using magnum primers to overcome this problem.

 

[ArchAngelCD]

Where you live the temps are not varying enough for you to worry at all. IMO anything below Zero and above 100 degrees is a place to start worrying.

The words temp sensitive are over used but of course this what happens on the Internet. Remember, the same commercial ammo is sold in Alaska as in Southern Texas, how sensitive could the powders be?

 

[Bart B.]

I and others notice that a round in a hot chamber for 30 to 40 seconds will shoot its bullet out faster and strike higher at long range than one that's in for 15 to 20 seconds. Hotter powder temp's produce higher pressures and velocities. At a thousand yards, I come down 1/4 MOA on the sight for every 30 seconds of chamber time for 308's; every 20 seconds for 30 caliber magnums burning 50% more powder.

Some at long range matches lay their ammo on the mat and it heats up from direct sun. Their last shots fired 25 minutes after the first ones need a few MOA less sight elevation.

It's the powder temperature, not ambient, that's important for bullet velocity uniformity. Ambient air temperature effects can be seen with ballistic software.

 

[wally]

Where you live the temps are not varying enough for you to worry at all. IMO anything below Zero and above 100 degrees is a place to start worrying.

This. Marketing departments need something to market


"Reverse" temperature sensitivity could be a design feature and not a bug or fluke. Hot air is less dense than cold air so having a higher velocity in cold temperatures would help compensate for the external ballistics effects of the air density change with temperature. However I doubt it matters a hoot at ranges less than 300 yards for rifles or 100 yards for handguns.

Bart B. makes an important point that the ammo temperature and air temperature can be very different depending on your shooting situation. One shot after sitting in a blind or tree stand for hours, the air and ammo will be pretty much the same temperature. Shooting a long high power match, if the ammo sits in the chamber very long between shots it likely will be significantly warmer than the air temperature.

 

[hdwhit]

I agree with ArchAngelCD that, in general, temperatures above zero and below 100 are not anything to worry about.

When I started reloading .223 Remington back in the 1970's there was a commonly reported caution that IMR-4198 if stored for prolonged periods of time below 10 degrees farenheit would suffer what amounted to freeze damage that altered its structure and resulted in increased pressures when later fired.

I had several hundred rounds of .223 that were loaded with IMR-4198 at about 94% of then-published maxmum and throughly frozen below zero degrees. When subsequently fired, velocities were indeed about 5% higher than unfrozen loads but the cases showed no sign of excessive pressure. From this, I concluded there was some merit to the reported temperature sensitivity of IMR-4198 but the increases in pressure were modest and not a cause for concern for loads that were below maximum.

 

[rayatphonix]

Kingmt, I live in the NC mountains. Most summer days in the 80's. I generally hunt down on the coast where we have considerably more deer.

 

[Stumper]

All propellants exhibit some temperature sensitivity. Some show a bit less than others. Mostly it is something that scarcely matters for most firearms uses. (Extreme long range shooters live in another world from the average). The only concern I have with powder and temperature sensitivity is with Blue Dot. It is known to drop a lot of velocity in shotgun loads in cold weather and to exhibit high pressure signs in magnum handguns when very cold. It is a useful powder and never caused me any grief but I dropped it and switched to others that don't show those effects since every now and then I do shoot in very cold temps.

 

[Decoy80]

I worked up a subsonic load this past summer with Ramshot Competition for 9mm. It did very well in the Mississippi heat and humidity. I had a couple hundred or so left over so last week decided to feed them to my old P89 Ruger. Much to my dismay the ammo would not cycle it in the cooler temps of winter. I agree that powders display different results due to temp changes. Ive been guilty of leaving the bolt open hunting with my first round in my pocketed hand in cooler temps, rifle cartridges deer hunting.

 

[LiveLife]

Bart B. makes an important point that the ammo temperature and air temperature can be very different depending on your shooting situation.

I agree. Reloads I tested on post #82 were loaded for velocity, accuracy and temperature sensitivity threads. Reloads were intentionally stored at ambient temperature and transported in a manner to maintain same powder temperature as ambient temperature - https://www.thehighroad.org/index.p...n-9mm-40s-w-45acp.799231/page-4#post-10338994

I agree with ArchAngelCD that, in general, temperatures above zero and below 100 are not anything to worry about.

Depends on your shooting application. For recreational range/plinking loads, probably not, but if your USPSA match loads were loaded to 125 PF on warmer days below 100F, they will likely not meet PF requirement on colder days above zero degrees F. I remember some match shooters kept their rounds in ice chest on hot summer days because they were using reverse temperature sensitive powders that lowered velocity on hot days.

Another thing to consider is efficiency of powder burn. At minor power factor with some powders, powder burn may be less efficient to produce consistent enough chamber pressures for optimal accuracy. Due to this reason, for certain powders some match shooters load at higher 130-135 power factor to improve accuracy.

There are many reloading variables that will affect accuracy. Temperature sensitivity of powder may not affect accuracy as much as neck tension and bullet setback for pistol rounds. Remember, it's not the finished OAL that matters but "chambered" OAL that will affect chamber pressure when the bullet nose slams on the feed ramp. Enough variance in chambered OAL and resulting bullet seating depth/setback will increase group size, likely overshadowing powder sensitivity and other reloading variables.

That's why I follow the notion of "Holes on target speak volumes". We can discuss all we want the suppositions about reloading variables but ultimately, it's the holes on target that will give us the most useful information about our loads. If adjusting certain reloading variable shrinks group size, then we are improving consistency of our reloads. Sometimes, my theories don't always translate to target. With certain powders and bullets, using longer OAL to reduce gas leak will improve group size. With certain powders and bullets, using shorter OAL to increase neck tension will improve group size.

 

[wally]

It did very well in the Mississippi heat and humidity. I had a couple hundred or so left over so last week decided to feed them to my old P89 Ruger. Much to my dismay the ammo would not cycle it in the cooler temps of winter.

Are you sure it wasn't your gun lube that stiffened and inhibited function in the winter temperatures? If it gets below freezing here, its all the radio and TV news can talk about so I don't have a lot of experience shooting at low temperatures, but one lube I used for a while on my Ruger MKII wouldn't cycle at about 40 degrees, but I persevered and once the gun warmed up after a couple of mags, it functioned fine until I was done.

 

[Bbear]

Here's one article on temp sensitivity:
http://www.rifleshootermag.com/accuracy-tests/fact-fiction-gunpowder-temperature-sensitivity/

And yet another:
http://firearmshistory.blogspot.com/2012/11/the-effect-of-temperature-on-ammunition.html

In my personal experiences, using RL 19 in one of my 25-06's, I worked up a very accurate load in mid-30 degree temps. That summer, with temps in the low 100's, the first round I fired locked up my bolt. Velocity increased by nearly 400 fps as well. So, it was back to the bench to pull the rest. The RL 19 is now fertilizing my garden.
I switched to 7977 and worked loads in the 100 degree range and found a great group and velocity. In the winter, with mid-30 degree temps, I lost less than 30 fps and accuracy was still sub-moa my rifle.

 

[jmr40]

Most powders will see anywhere from 1-2 fps velocity change for each 1 degree temperature changes. It works both ways. A load chronographed at 40 degrees will be 60-120 fps faster at 100 degrees. Ammo stored inside a vehicle in summer heat could reach 140-150 degrees and if fired when hot could be over 200 fps faster and dangerously over pressure. Living in GA this is more of a concern than shooting in cold weather.

If you develop a load at 80 degrees it could be 50-100 fps slower at 30 degrees. At normal ranges not really enough to worry about, but at longer ranges 100 fps could make a difference. If you start shooting below 0 then the difference is more dramatic.

If given an option I prefer to buy temperature resistant powders. You'll still see velocity changes, but in the .5 fps/1 degree range.

 

[Caliche Kid]

Chemistry of reaction rates, kinetics, dictates that chemical reactions, powder burn rates, are temperature dependent. Rates are higher at higher temperatures. This cannot be avoided. The rate dependency is exponentially related to the activation energy as expressed in the Arrhenius equation. Since all current powders are utilizating NO2 bond breaking for propulsion as in nitro glycerine and nitro cellulose combustion, there should be very little difference. Far and away the controlling factor is the size of the fire. This is why slow burning powders like H 4350 seem to be more temperature insensitive, there is a lot of it being burned. Mostly this is hype to sell powders. If it shoots good in your rifle, try it at the lowest and highest temperatures that you are likely to hunt in and if your zero stays constant, don't worry about this. If you are a long long range shooter and you have corrected for air density, etc. then you might want to chronograph your load at the temperature extremes and factor this into you hold over.