I have read here about how some powders change quite a bit with temp change but I never seem to know which ones. My two main powders are W231/hp38 and WSF. These are in 9mm with a 124 rn RMR plated bullet. Charges are 4.3 and 4.5 gr. respectively at 1.130 oal. I'm shooting uspsa and steel challenge. Thanks
Will these two powders change poi with temp change?
- Thread starter egd
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I now think most powders shoot bullets faster when they're at higher temperatures above ambient ones. At ranges less than 100 to 200 yards, the difference may be hard to detect with hand guns. At longer ranges with rifles, it's easy to see and some people come down a click (1/4th MOA) on their sights for every 20 to 30 seconds a round sits in a hot chamber. If they don't, that round will impact higher than desired.
Chronographing fixed handguns is the best way to check that out.
Contact the powder companies then ask them.
Updated based on post #3.
Chronographing fixed handguns is the best way to check that out.
Contact the powder companies then ask them.
Updated based on post #3.
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Blue68f100
Member
NOT All powders. Some are reverse sensitive like WST. It produces higher velocities at colder temps.
The 2 you list are what I do not consider temp sensitive. But the only way to confirm is load some up a put some in the freezer and some in the heat, then run them over the crony.
LiveLife
Member
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)
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
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)
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
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Jim Watson
Member
Chemical reactions are generally "temperature sensitive."
I wish a ballistician would explain what is going on with these "inverse temperature" sensitive powders.
I wish a ballistician would explain what is going on with these "inverse temperature" sensitive powders.
Well then, I sit corrected. Thanks for that.
LiveLife
Member
Since action pistol matches like USPSA do not require precision of bullseye matches, most match shooters tend to develop match loads that meet required power factor with "good enough" accuracy.
If your double taps hit 0.5" higher, I doubt your score will change much.
As Bart posted, I doubt you'll see much difference at 7-25 yards USPSA targets are set at.
If your double taps hit 0.5" higher, I doubt your score will change much.
As Bart posted, I doubt you'll see much difference at 7-25 yards USPSA targets are set at.
wally
Member
Unless you are winning 2700 Bullseye matches or long range silhouette matches I doubt it'll make much practical difference with handgun loads.
We don't get really cold here and when we do I don't go shooting, but my reloads see 40-100+ degree temperatures in a year of shooting. I've never noticed enough difference to matter with my reloads using Unique (I've standardized years ago).
For rifles at under 200 yards, 100 fps velocity change one way or the other doesn't matter much unless you are winning benchrest matches. At longer range, I think the velocity change effects are swamped by the aerodynamic factors that also change with temperature. Play with one of the on-line ballistics calculators (http://www.jbmballistics.com seems good) and change muzzle velocity and temperature to see what the effects might be at the distances that matter to you.
To me this is a relatively "new" mentioning of an effect that has existed since the beginning of shooting and little more than a way to get you to worry about something minor so you'll pony up more dough for fancy new ammo or powders. YMMV.
Chemical reactions generally follow the Arrhenius equation. k=A*exp(-Ea/R*T) where k is the rate coefficient, A is a constant, Ea is the activation energy, R is the universal gas constant, and T is the temperature (in kelvin). If the activation energy is independent of temperature this usually means a doubling of rate with a 10 degree (kelvin) change for biological environmental condition reactions. I suspect the activation energy of the powder coatings do vary with temperature, but at the extreme conditions of burning gunpowder I suspect all sophomore chemistry knowledge is out the window.
We don't get really cold here and when we do I don't go shooting, but my reloads see 40-100+ degree temperatures in a year of shooting. I've never noticed enough difference to matter with my reloads using Unique (I've standardized years ago).
For rifles at under 200 yards, 100 fps velocity change one way or the other doesn't matter much unless you are winning benchrest matches. At longer range, I think the velocity change effects are swamped by the aerodynamic factors that also change with temperature. Play with one of the on-line ballistics calculators (http://www.jbmballistics.com seems good) and change muzzle velocity and temperature to see what the effects might be at the distances that matter to you.
To me this is a relatively "new" mentioning of an effect that has existed since the beginning of shooting and little more than a way to get you to worry about something minor so you'll pony up more dough for fancy new ammo or powders. YMMV.
I'd wager its the coatings that prevent the powder granules from clumping and detonating and play a large effect in controlling the "burn rate" (fast vs. slow is measured in tens of microseconds) some may get easier or harder to ignite with temperature leaving the possibility of the temperature coefficient "inverting".
Chemical reactions generally follow the Arrhenius equation. k=A*exp(-Ea/R*T) where k is the rate coefficient, A is a constant, Ea is the activation energy, R is the universal gas constant, and T is the temperature (in kelvin). If the activation energy is independent of temperature this usually means a doubling of rate with a 10 degree (kelvin) change for biological environmental condition reactions. I suspect the activation energy of the powder coatings do vary with temperature, but at the extreme conditions of burning gunpowder I suspect all sophomore chemistry knowledge is out the window.
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Blue68f100
Member
Looks like a lot more pistol powders are reverse sensitive than I remember. Thanks for posting. Here in Texas is why I probably did not notice any difference. Not the huge swing like some parts of the country. Then like said, you have to be a good enough shot to even know there is a difference. Which means better eye sight than I currently have. All sights are a blur for me, so I must use some sort of optics/red-dots for aid. We are suppose to get a 50+ deg temp swing between today and tomorrow.
wally
Member
Actually for powders a reverse sensitivity could be a feature, not a bug. If the velocity goes up with lower temperatures, it could help offset the aerodynamic increased drag at lower temperatures.
Quick sample from a ballistics calculator:
A .308 load I use with a 300 yard zero and MV of 2450 at 95 degrees has a drop of 6.9" at 350 yards. Changing the temperature to 35 degrees increases the drop to 7.2" and increasing the MV to 2550 at 35 degress reduces the drop to 6.6". Not a major effect but if you start going beyond 500 yards it could start to really matter.
Quick sample from a ballistics calculator:
A .308 load I use with a 300 yard zero and MV of 2450 at 95 degrees has a drop of 6.9" at 350 yards. Changing the temperature to 35 degrees increases the drop to 7.2" and increasing the MV to 2550 at 35 degress reduces the drop to 6.6". Not a major effect but if you start going beyond 500 yards it could start to really matter.
Blue68f100
Member
Good point and during the winter months your normally wearing more clothing too.
Dog Soldier
member
Most long range shooters have taken advantage of temperature. It is common to expose loaded cartridges to direct sun light to warm up the propellants. This can reduce the arch making a difference in POI.
When the Temp drops below 40 Degrees using a magnum primer can accelerate the propellant. A hotter spark plug can help.
These theories/Hypotheses, go back to the days of the Buffalo hunters. My Sharps .45-110-500 is interesting to chronograph in the changing seasons. If you have a minute read the link. Thanks guys.
http://www.longrangebpcr.com/Accuracy.htm
When the Temp drops below 40 Degrees using a magnum primer can accelerate the propellant. A hotter spark plug can help.
These theories/Hypotheses, go back to the days of the Buffalo hunters. My Sharps .45-110-500 is interesting to chronograph in the changing seasons. If you have a minute read the link. Thanks guys.
http://www.longrangebpcr.com/Accuracy.htm
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