How does "temperature sensitivity" manifest itself?

[LocoGringo]

So I'm doing some reading and one of the compromises listed for handloading is "temperature sensitivity". I chose H-414 as one of my main powders for loading 7mm-08 in the mid to heavy bullet range, but its main issue is "temperature sensitivity". Ok, but what does that mean? Is muzzle velocity noticeably different, do groups open (or close, depending on loading temps vs. shooting temps)? How can you tell it's temperature sensitivity versus some other issue like shooter flinch, seating depth, varying charge weights, etc.?

I haven't actually used the powder yet, but I've gotten a couple pounds of it and expect to use it for the Hornady 162 grain SST bullets I have. I'd like to know what to look for with respect to temperature sensitivity.

 

[Varminterror]

Muzzle velocity changes. For some loading methods, that seems to allow loads to slip out of nodes and groups and/or velocity consistency can scatter, as well as shifting trajectory downrange.

H414 is about as bad as any powder gets for temp sensitivity.

How do you tell the change was temp sensitivity and not something else? Well, flinches don’t cause MV to change by 50fps from a previous benchmark. Charge weight consistency won’t change if your dispensing method hasn’t changed, so if you have a load shooting a 24ES at 2950 and suddenly it’s shooting a 24ES at 2875, or shooting a 45 ES at 2900, and the only thing which changed was the weather you can be sure it’s not a charge weight consistency issue. Seating depth isn’t going to change unless you change your die, and won’t push your MV up and down with temperature.

Most obvious indicator. Cold ammo kept on the bench or in your bag shooting slower than ammo kept in your pocket.

 

[Bronco72]

Well, if you develop a MAX in cold temperatures it may well be unsafe in hot weather, as in problems, blown primers, ruptured cases or worse! I develop my max loads in hot weather then learn how they perform in the cold.
I'm just sayin.
If you want a more scientific explanation I am sure someone will come along

 

[LiveLife]

Most powders have "normal sensitivity" where velocity increases as ambient temperature (more specifically powder) increases.

Some powders are more "temperature sensitive" meaning velocity increase is higher than typical compared to other powders. And some powders are "reverse temperature sensitive" meaning velocity decreases as ambient/powder temperature increases.

When you are range testing "temperature sensitive" powder loads in range conditions where temperature fluctuation/rise/fall can be a factor, you may want to use ice chest/insulated box or multiple cardboard boxes to prevent sunlight on hot day from heating up the powder charge inside brass cartridges (Remember brass is copper/zinc alloy and copper is an excellent conductor of heat).

And once your chamber gets hot, prevent "cooking of a round" by leaving a chambered round too long to soak up heat which will undoubtedly affect muzzle velocities and likely change/increase group size.

BTW, some examples of temperature sensitive/reverse temperature sensitive powders - https://www.thehighroad.org/index.p...s-and-discussions.778197/page-7#post-10117881

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
- Promo
- WST
- Solo 1000
- N320 (but some claim reverse temp sensitivity)
- SR7625
- Universal
- WSF
- Silhouette

 

[Varminterror]

For comparison:

 

[LocoGringo]

@Varminterror , thanks for posting that list. Seeing RL15 so far down that list might explain why my handloaded (not by me, but a professional) .223 ammo wasn't so accurate recently. I was very surprised and disappointed to see that ammo MUCH worse than my everyday 3-gun competition ammo (PMC Bronze).

Wow, that is very informative. Thanks again.

 

[LocoGringo]

Here's a YouTube video that illustrates temperature sensitivity:

Winchester StaBALL 6.5 - Temperature sensitivity test - YouTube

Do y'all agree with his procedure and findings?

I just happened to find this video because I'm doing a little research on StaBall 6.5 since someone recommended it for my 7mm-08. It's looking pretty good...

 

[Ru4real]

My advice is to
1. Develop a load that shoots well
2. Test load in all conditions to see if it’s always good

Don’t sweat “stable powder” until proven unstable. Changing POI is not a measure of bad. Larger groups is.

Example. RL22 is not comparatively stable. But in my 7mm it shoots tight groups at 100F and -20F. The POI shift is fixed with two clicks on the elevation turret. Not a big deal.

 

[Varminterror]

Don’t sweat “stable powder” until proven unstable. Changing POI is not a measure of bad.

The POI shift is fixed with two clicks on the elevation turret. Not a big deal.

Missing by 7.2” is kinda a big deal to me.

When I shot Leverevolution in 6 Grendel, instead of 8208, it meant if I didn’t correct MV for temperature at a match in March where we started shooting at 29F and ended up in mid 60’s, I would have sailed bullets 12” over POA at 1000yrds by the end of the match compared to my MV measured at the beginning of the match. I don’t like missing by 12”. Shooting 8208, I only have 4” shift - I account for temp change in my calculators, but putting 4” at risk instead of 12, just by buying a different powder, makes a lot of sense.

If you’re shooting at short range and not competing, sure, “two clicks” might not matter, and you achieve your goal. Not everyone will.

 

[Ru4real]

Missing by 7.2” is kinda a big deal to me.

Apologies for you missing. I don’t. That’s the point of testing loads. I think we both agree on this point.

I make the adjustment before I have to make the shot. I understand in competition, adjustments are usually avoided.

In fairness to your point, my RL22 loads wouldn’t be my first choice if I wasn’t certain. My IMR7977 or Retumbo loads would be. Those are tested too, and like your chart shows, they also have little POI shift hot to cold outside. So little in fact, I’m not sure if the POI shift is due to powder or air density.

 

[Varminterror]

I’m not sure if the POI shift is due to powder or air density.

Pretty simple to measure both.

 

[kalielkslayer]

Loco,

H414 was the most accurate powder in my wife’s 7-08. With Hornady 139 he SSTs, Barnes TTSXs and Nosler Accubonds.

I compared it against RL19 and IMR 4350.

Each time H414 took the award for accuracy.

Loads were developed in the summer. She killed her bulls in October at 10,000 feet, her antelope in early September at 5,500 feet.

I can’t argue it’s not temperature sensitive. But I’ll always go with the best groups, and they seem to work.

So is this the same with W760? since it’s the same powder?

 

[LocoGringo]

Loco,

H414 was the most accurate powder in my wife’s 7-08. With Hornady 139 he SSTs, Barnes TTSXs and Nosler Accubonds.

Which TTSX...120, 140 or 150? I also have 500 139 Hornady Interlocks that came with my Hornady kit back when they ran a special a looong time ago.

I'm loading 120 TTSX for my son's 7-08 with BL-C(2) for low recoil, but relatively full case. I have a load that shows a lot of promise. 43.3 grains that has a 5-shot group measured center to center at about .763".

 

[Ru4real]

Pretty simple to measure both.

How so? So far I can only come up with guesses or estimates but no measurements.

Ballistic calculators with air density compensation give me a number, and shooting in condition gives me a number. But the difference between the two being powder related is still an estimate.

 

[Varminterror]

How so? So far I can only come up with guesses or estimates but no measurements.

Ballistic calculators with air density compensation give me a number, and shooting in condition gives me a number. But the difference between the two being powder related is still an estimate.

Powder sensitivity to temp change = velocity —> chronograph

Air density as an influencer upon trajectory = density altitude —> weather meter (Kestrel)

Toggle either independently in your ballistic engine and you’ll know exactly how much either is influencing POI shift.

 

[EricBu]

I try to avoid temp sensitive powders in my hunting loads, but sometimes you can't and all powders are temp sensitive to a degree (see what I did there?), it's a matter of how much. Some of the things I do to mitigate it...set up a target in my hunt area and verify zero, make adjustments accordingly. Keep the ammo as stable temp wise as possible...for example, if you are in a heated camper, and you're hunting in 5 degree weather...don't keep your ammo in the camper, or your gun for that matter...because moving it back and forth from 70 degrees to 5 degrees will change it's performance. Same with the gun, gun is even worse in super cold weather, you'll get condensation in the barrel, which may turn into an ice plug, so I rod my gun everyday in the field and keep it and my ammo in the truck so it's always cold. In the summer, be mindful of the same...if your truck is 130 degrees in the sun, and you're ammo is sitting in there...or when you're at the range keep your ammo from sitting in direct sunlight. Just little things like that. And of course, size matters, lol. Lighter, higher velocity rounds, tend to be more sensitive, where as big and slow may not even be noticeable. Then the last thing to remember...don't do your load development in winter, then happily hit the range in the summer...ammo in hot truck, then sitting in sunlight........now you've crossed extremes with the load development and you're perfect .5 MOA load you worked up in January is suddenly blowing primers and hard to extract.

 

[BBarn]

I read years ago in Western Powder's FAQs that a powder's temperature stability wasn't constant across applications. They claimed a powder that was fairly temperature stable in one cartridge might be considerably less temperature stable in a different cartridge. And vice versa.

 

[Engineer1911]

The Manifestation of Temperature Sensitivity:

Found accurate safe loads for 222 Rem and 25-06 prairie dog ammo. 1/2" groups at 100 yards, primer was not flattened, velocity was in the middle of the expected range, bolt handles lifted easily with one finger. Temperature was about 70° F and I was shooting in the shade (under the firing line roof). Rifle barrel never even got warm.

Out in the prairie dog patch, the same ammo had flattened pierced primers, recoil increased, bolt handle became difficult to lift, and was not as accurate. There was no shade (I am shooting in a pasture), very bright late June sunshine, temperature is a balmy 92° F with 10 MPH breezes and 12% humidity. After sitting in the sun for 20 minutes, either gun barrel was hot to the touch before starting to shoot. I would call that 'temperature sensitivity'.

 

[Palladan44]

When using blue dot

 

[Bfh_auto]

Loco,

H414 was the most accurate powder in my wife’s 7-08. With Hornady 139 he SSTs, Barnes TTSXs and Nosler Accubonds.

I compared it against RL19 and IMR 4350.

Each time H414 took the award for accuracy.

Loads were developed in the summer. She killed her bulls in October at 10,000 feet, her antelope in early September at 5,500 feet.

I can’t argue it’s not temperature sensitive. But I’ll always go with the best groups, and they seem to work.

So is this the same with W760? since it’s the same powder?

It's the same in 260 Rem. I just did a load workup at the temperature my wife usually hunts in. It's definitely a velocity king. But it takes more powder to get the velocity back to what it is in 90 degree weather.

 

[taliv]

assuming you're not running into safety issues by working up loads in january and then shooting them in august...

the key is really just for long range precision shooting and primarily the issue is working up loads at the range on beautiful days and then going to shoot something when it's 10* or such, and the powder just has a lot less energy at that temp and so you get lower muzzle velocity.

Back in the day, I used to shoot 260AI and really loved R15 which is one of the most temp sensitive. On the chart it's 1.52 but I measured it at 1.73 iirc and simply put that number in my ballistic calculator and it adjusted for me no problems. I never had an issue.

Uncorrected though, a 70* to 20* temp drop of 50* x 1.73 is about 87 fps drop. at 600 yards, that's a change of .3 mil which would mean a miss on a 12" target.

 

[Varminterror]

I read years ago in Western Powder's FAQs that a powder's temperature stability wasn't constant across applications. They claimed a powder that was fairly temperature stable in one cartridge might be considerably less temperature stable in a different cartridge. And vice versa.

The needle doesn’t swing very far. Ball powders and double base powders with high nitroglycerin content will always be more temp sensitive than single base powders.

I’ve heard a lot of different suppositions about various influences, some of which make more sense than others, but have also heard opposite “truths” - such as lower operating pressures being less sensitive to temp because the pressures don’t spike as violently, but alternatively that higher operating pressures are less sensitive because the percentage influence is so much lesser than the total pressure (law of large numbers, effectively). I’ve heard slower powders are less apt to be sensitive, I’ve heard smaller charges are less apt to be as sensitive, I’ve heard magnum primers can make up for sensitivity… by and large, I’ve not been able to prove ANY of these to be true, but I HAVE been able to watch my chronographs change more with more sensitive powders and change less with less sensitive powders… so as a rule, I try to live life with Varget, 8208, H4350, H1000, and Retumbo in almost all of my cartridges I load, and I don’t have to worry as much about temp changes - quick input in the calculator, or use their reference data and be sufficiently close, and I’m on target.

 

[AJC1]

Because I failed to properly plan I'm just shooting regular extruded single base powders. Imr powders aren't fancy but middle of the road in about every way.

 

[jmr40]

It's complicated. Some powder that is stable in one cartridge, may be less so in another. For example Varget and RE15 are both pretty stable in 308, but less so in other cartridges.

I don't know of any scientific studies that where you can read of the results. But I've read posts from shooters who have done some informal testing and posted the results online. John Barsnses, who has written for several gun magazines has done some testing and posted about it over at 24hourcampfire seems a reliable source.

Based on what I've read expect 2-3 fps velocity change for each 1 degree temperature changes for sensitive powders. The less temperature powders are usually around 1/2 fps velocity change for each 1 degree. And hot weather can increase velocity, not just decrease it in cold temperatures.

Most published data is at 70 degrees. At 20 degrees that could be 100-150 fps slower for some powders and only 20-30 fps with others. At ranges under 200 yards losing 150 fps probably won't matter. But at longer ranges it could. At typical 308 velocities there would be about 1/2" more drop at 200 yards with a 2650 MV vs 2800 MV. But at 500 yards it would be 5" more drop.

 

[Palladan44]

This is just yet another reason to load conservatively, and not to hot-rod cartridges.
Or, another reason of many that handloading data isn't what it used to be. Lots of fudge factor, factored in.
I will admit that most of my reloading "red flags" have come in handloads that are at or near the top end of the envelope, using data from the days of old. Which is why I don't push the envelope anymore