powder temperature sensitivity

Discussion in 'Reloading' started by drpbroun5, Jun 2, 2008.

  1. drpbroun5

    drpbroun5 Well-Known Member

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    Guys,
    I have heard alot about temp sensitivity in various powders. Has anyone done any testing of different powders to see how much temperature affects each? I have not been able to find any data on this topic. I did a search on LRH and saw some discussion regarding specific powders but none that compared several or multiple ones. If anyone knows of some data on this, I sure would like to get it. Thanks.
    Paul
     
  2. goodgrouper

    goodgrouper Well-Known Member

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    Absolutely! There have been many tests on this subject. Many have been published and some data is contradictive but I'll give you my own personal results.

    As far as brands go, here's my list from most temperamental to least:

    1. Ramshot (because they are all rifle ball powders)
    2. Winchester (because they are all rifle ball powders)
    3. Accurate (because they are mostly rifle ball powders)
    4. Alliant
    5. IMR
    6. VV
    7. Hodgdon


    As for individual powders, my list is this: (I'm not going to name each powder here, just a few of the best and worst and a few of the ones in the middle)

    most temperamental to least:

    H380
    H414
    WW748
    AA2460
    WW760
    H335
    RL25
    RL22
    IMR4198
    AA4350
    VV550
    H4895
    IMR4350
    IMR4831
    IMR7828
    N165
    H1000
    H322
    H4831ssc
    N170
    N133
    Benchmark
    Varget


    Even though some of the powders listed towards the bottom of the list are great for weather insensitivity, they still exhibit a need to tweek with the charge slightly in temperature changes to maintain a certain pressure. Despite some claims by some manufacturers that their powders will shoot the same from 20 below to 120 above, no powder is perfect. Temperature changes all combustables combustion. Period. It is unavoidable no matter what "coating" you use on the powder. And all powders show markedly different characteristics once the temp gets to and above 80 degrees. Loads worked up above 80 will still work accurately as long as the temp stays above 80 degrees. But loads worked up below 80 degrees F do better shot up to around 75 degrees. Or in other words, loads worked up in cool weather hold their node for a longer temp range than loads worked up at or above 80 degrees F.

    I'm not sure why 80 degrees is the unlucky number, but I have seen this be the fulcrum of load development time and time again with every brand and make of powder--especially ball powders.
     

  3. phorwath

    phorwath Well-Known Member

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    GG,

    Wow. A lot of useful information on powders here for us. I'll be printing this one out and placing it on my reloading bench, based on how much time you've logged reloading and fine tuning reloads for your and other's rifles. Thanks for sharing this with us.

    Not to steal this thread, but I tried RL 22 and IMR 7828 in my 300 WM after PM'ing with you. It look's like IMR 7828 is the keeper with the 210 Bergers for a low ES/SD load. I had about 5/8" vertical spread over 5 consecutive loads (over 2 gr - in 1/2 grain powder increments) at 300 yards. I also had a great velocity pause in the middle three of these five consecutive loads. 73.5, 74.0, & 74.5 gr IMR 7828. MV ~ 2970 fps. Now I need to shoot and confirm data once again at longer range. Thanks for your help.

    Paul
     
  4. J E Custom

    J E Custom Well-Known Member

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    Good post ,

    Good grouper is dead on as far as i'm concerned .

    My results were the same. Example= In my 7/08 one of
    my best loads is 120gr balistic tip,49.5 grs H 414 ,CCI 250br2
    at 3010 @ 65 degrees (but during the summer around 100 o
    the velocity jumps to 3154 ) 144 ft/sec faster with an incress of
    35 Degrees.

    The next load is varget and velocity only increses 7ft/sec with
    the same conditions and velocity.

    Hear in Texas the temp can range from 15o to 70o in just one day
    of hunting so I have changed most of my loads to hodgdon Extreme
    powders.

    J E CUSTOM
     
  5. rocky_lange

    rocky_lange Well-Known Member

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    Varget

    I live in Alabama and developed my hunting load in 80 degree weather. Rifle is an AR10A2, .308 Winchester 20" barrel. Bullet was a 168gr Barnes TSX over 45gr VARGET C.O.A.L. to fit magazines and crimped using Lee Factory Crimp die. For my purposes, velocity was not an issue as I use iron sights and was using this rifle for drives where longrange shots were not expected. From a mechanical benchrest style front rest and rear bag I could shoot 5 shot sub 3 MOA groups from 100 yards. When I arrived in Wisconsin in November for the hunt, I shot at the range from a "tackdriver bag" front rest and rear bag in 30 degree weather and still shot 5 in sub 3 MOA. More importantly, I noticed no evidence of a shift in point of impact.
    Dead on at 80 degrees, dead on at 30 degrees. I love my VARGET!

    Rocky
     
  6. jeffbird

    jeffbird Well-Known Member

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    Temp Adjustment RL22

    In 7WSM with 175/6's and working on 1000 yard loads, I tested a substantial number of loads with RL22 over a range of temperatures. It definitely is effected by temperature, but it is very predictable. I work up all of my loads in the heat of summer, so if they are safe then, they are good to go year round. My loads were developed at 95 F. To calculate the velocity drop in my loads, I would take the temp 95 minus actual temperature, say 45F for an example. That is a 50 degree drop MULTIPLY BY 0.8 = 40 fps drop. It is very predictable and consistent. I have since changed over to MagPro for the 7WSM and am working out a similar formula, but it does seem less sensitive.

    Hope that helps.
     
  7. Shawn Carlock

    Shawn Carlock Sponsor

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    I am in agreement with GG on 80 deg being the piviot point I too have seen this with many powders. I have been a long time Hodgen Extreme powder fan. I also agree that even the best powders are sensitive to some degree, some less than others. I have in addition noted that the combination of components effects temp sensitivity it is not just a powder issue. H1000 is slightly more sensitive to temp in a 300 RUM with CCI250, and 200 NAB's than it is with a 338 Edge with CCI 250's, and 300 SMK's. I have also noted that primer choice with effect this also, in the 338 Edge 215M primers made the combo more temp sensitive than the CCI250's did. I have seen these differences in multiple rifles. In the end it takes a little work to find the best temp sensitivity combo. I use a laser thermometer in cold conditions to do this. I shoot a controll group at ambient temp (20-40 degrees) then warm up a number of rounds to 60 degrees and 100 degrees to shoot comparison groups. Ultimately the best I have come up with is a consistant 18-20 fps spread from 24 degrees to 100 degrees. I was only able to do this with one caliber and combination. The rest varied from 30 to almost 250 fps.
    You can do like Jeff does and make a temp / velocity chart and enter the velocity for the temp your in but that to me is just one more thing to have to screw with. If you are using a temp sensitive combo you can change velocity by having a round in a warm rifle barrel for a minute despite the ambient temp being cooler. I have seen this "barrel warming" of the round change the velocity with as little time as 30 seconds in the barrel on sensitive loads. Good question DRPB and good responses.
     
  8. eddybo

    eddybo Well-Known Member

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    Great information thanks for sharing.
     
  9. goodgrouper

    goodgrouper Well-Known Member

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    Glad to hear you got the gun figured out. Sounds like it's a shooter. Have some fun with it!
     
  10. goodgrouper

    goodgrouper Well-Known Member

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    I would also like to add that some powders show remarkable stability through a wide temperature range but then all of a sudden will go crazy when a certain temperature is reached. In my first 6ppc barrel of '07, it showed amazing accuracy with H322 when I first tinkered with it. THis was in January and I was working up loads at 10 degree temps. It was shooting in the "zeros" quite frequently and did so all winter and spring. Then when temps got to about 85 degrees just in time for our first local match, the powder went crazy and pressure spiked so bad that it was tough to hold a group under a .4" at 100 yards! I even dropped the charge down until I was getting speeds similar to the winter charges and it still wouldn't shoot well.

    On the flip side of that coin, I had a lot of N133 that year that shot so so in the same barrel in the cold but never had groups go much under 1/4". I stoked up the charge to the point that it was hurting my brass and the groups got rounder but no smaller. I lowered the charge and the groups got vertical and larger. Then when the H322 went to pot in summer, I went back to the N133 and it kept shooting better and better the hotter it got. The velocities from winter to summer with the same load of N133 never were more than about 50 fps difference, but something about the warmer weather just brought out the best in N133.

    A guy could spend a lifetime with a hundred powders and a thousand calibers and never figure all this stuff out!
     
  11. old_heli_logger

    old_heli_logger Well-Known Member

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    Awesome post!!
    Thanks!
     
  12. noone

    noone Member

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    I was using 68.5 grains of IMR4350 in a 300 Win Mag, Winchester brass, Fed 215 primers, and a 190 Sierra match king. In winter, the load is very consistent, accurate, and gives 2960 FPS. When the temperature hits around 80-85, the velocity jumps to over 3050 FPS, so after 2 shots over the Chrono, I decided to save the rest of that lot of ammo for next winter's shooting. And it worked great again. I have a few months before temperatures start getting too hot for me to want to use that load again.
     
  13. LouBoyd

    LouBoyd Well-Known Member

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    Knowing temperature coefficients for various powders isn't easy to translate into actual velocities versus temperature, but it's pretty easy to bring two small ice chests and a thermometer to the range with hot and cold water in them. When you're working up loads and have one you like you can test them by putting them in a small ziplock in the bath long enough for them to come to the water temperature (about 15 minutes). Then shoot them immediately over a chronograph and record the velocty and water temperature. It's the powder temperature at the time of ignition that matters most though the chamber and barrel temperature have some effect. Of course the air temperature also affects air density which determines the trajectory.

    Some ballistic computers allow you to enter velocity and temperature points and they're automatically measure the temperature and proved the corrected velocity and trajectory solution.
    They assume though that the ammo is at ambient temperature which may not be the case.
    The Kestrel 4200 with Horus Atrag software has the capability.
     
  14. Rugerdiggs

    Rugerdiggs Well-Known Member

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    [ame="http://www.youtube.com/watch?v=aWg92Nuob3A"]Shooting Tip Temperature Stable Powder - YouTube[/ame]

    this is a pretty good video i watched over this topic and they went pretty far extremes with it, they may be a little on the hodgdon side but it does shine a little light