Powder Temperature Sensitivity

Discussion in 'Reloading' started by vintec, Jan 24, 2009.

  1. vintec

    vintec Well-Known Member

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    I have found plenty of burn rate charts, but where can I find a chart the sates the temperature sensitivity.

    Also, what are the expirences that you guys have with ball powders vs stick powders sensitivity, and or how clean they burn.

    Thanks

    Vince
     
  2. ol mike

    ol mike Well-Known Member

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    Hodgdon extreme siries powders

    Vitv one hundred series

    Very generalized answer -too many variables.
     

  3. johnnyk

    johnnyk Well-Known Member

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    Vince,
    To my knowledge there isn't a chart which list or shows the info you desire. Hodgdon used to show this in their free little load data booklets. It would show the velocities of H4895 Extreme along side IMR4895 and other similar burn rate powders at 30 and 70 degree Fahrenheit. I haven't seen these in awhile, but I haven't been looking. I'd check their website. (www.hodgdon.com)...JohnnyK.
     
  4. Slim_T

    Slim_T Member

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    I am also interested in this type of information. I shot a practice F-class match today at Quantico MCB. When we started it was 10 degrees F outside and I left my ammo in the truck. I worked the pits in the early hours and didn't shoot until noon. So my ammo was around 20 degrees F (guessing) when I started. At 1000yds I shot cold ammo and I was darn near hitting the ground in front of the target. I adjusted 3 moa from my ballistic table to get x-ring. We had a 20 min cease fire and I left my ammo and rifle in the sun. The rifle felt nice and warm on a cold day and so did the ammo. My first shot after the cease fire was about 10in high. I adjusted down 1 moa and again started hitting x/10 ring. I do not believe that the wind changed or that I changed my shooting position significantly. So..I believe that the ammo warming up in the sun changed my point of impact 10 inches at 1000yards. My ballistics table was for 35F, but what it did not account for was the reduction in velocity due to the powder temp. I changed the ambient temp in my ballistics program to reflect the 15F difference and the drop was only slightly affected (8 inches). I then adjusted my muzzle velocity down until the 1000 yard drop was about what I had experienced at the start of my 1000yard shooting. The velocity change was 50fps reduced.

    So..I would like to find out what type of velocity change can occur due to temperature change of the power at the time of ignition.

    If I cannot find this type of information I will begin to experiment with warm and cold round over a chronograph.

    Slim
     
  5. vintec

    vintec Well-Known Member

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  6. Michael Eichele

    Michael Eichele Well-Known Member

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    It would be hard to develop a chart since so many variables go into the sensitivity of ANY powder. Things like case capacity, load density, bullet weight and cunstruction over the charge, twist rate in relation to the bullet used, free bore, and of course what spread of temperature youre shooting in.

    You will use some powders that are not famous for insensitivity and you might find that in your circumstances the difference with 80 degrees of swing is minimal when another shooter with other circumstances finds a HUGE increase or decrease in velocity. You cannot accuratly predict temperature sensitivity and IMHO too many shooters place too much importance on this. Find a good load, learn how much it increaces and decreaces in a given temp spread and BE HAPPY! None of us should be pushing a load to the max where a few degrees sends the load over the line.

    Just my .02 cents
     
  7. distantfoe

    distantfoe Well-Known Member

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    I believe temperature sensitivity is also more apparent in overbore calibers.
     
  8. MagnumManiac

    MagnumManiac Well-Known Member

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    Unfortunately, as stated above, the info you require just isn't out there.

    I can tell you for certain that Alliant powders are the worst for increasing/decreasing in power released with changes of temperature, and the best for not showing swings in power released are Hodgdon Extreme powders, most ball powders are stable until extreme cold/hot situations show themselves.

    One thing is for sure, if you work up loads in cooler months with Alliant powders, you will most likely run into trouble in the warmer months, I have had blown primers with a load worked up in winter, and then used in spring, a temp change of only 10 degrees C, go sky high in pressure causing me to abandon shooting for that day until I adjusted the powder charge.

    The only way to know what a powder will do in fluctating temps is to test it at varying temps.

    Cheers.
    MagnumManiac.
    gun)
     
  9. Michael Eichele

    Michael Eichele Well-Known Member

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    Tell that to my 300 RUM. I have tested her with RL-25 with 20 FPS difference from 75ish to -2 degrees F.

    Alliant isnt as sensitive as you may be led to believe. I have seen similar results with my 308 in RL-15 and anotehr 300 RUM barrel I used to use. Granted going from 75 to 110 may be a different story. For me and most other hunters, I wont be hunting in 110 degree air and If I had to, I dont push my loads to the max anyway so it would make little difference in the excessive pressure department. For most hunters, they develop their loads in fairly warm air and hunt in much cooler air.

    On the flip side of the coin, I know others who have experianced 100+ FPS in a 80 degree swing with RL powders. It just isnt predictable. Does this meen that Alliant is the MOST sensitive? Hardley. This is why one should develop a load their rifle likes best and go from there. Rifles are not biased about ambient temperatures like we are. They are harmonicaly biased though. This should come first in a load selection. You can always learn how much difference there is in an 80 degree spread and adjust you palm program accordingly. Harmonics come first. If you end up with a minimal affected load, then that is a bonus.
     
    Last edited: Jan 27, 2009
  10. Slim_T

    Slim_T Member

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    I believe the thought was that a chart or relative performance index (RPI) or powder temperature sensitivety would be a useful tool. Certainly, each instance of a bullet-rifle-load combination is going to produce different results, but a RPI allows you to gain an idea of performance and can assist in selecting a power before you spend much time investigating it. Similar to the use of a burn rate chart. RPI charts are quite common in the aircraft and auto industies.

    Having said all that, as you mentioned, I intend to characterize the temperature versus velocity of my 300 wsm load (using reloader 19) so that I can better hit the target and game. I'll post the data as I gather it.
     
  11. Mikecr

    Mikecr Well-Known Member

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    I'm sure it depends on loads, but I've found IMR to be less sensitive than Hodgdons pretty much across the board. Personally, I think Hodgdon's marketing is a bunch-o-hooey without real basis.
    That said, I use them, and I'm glad for their offerings.
     
  12. MontanaRifleman

    MontanaRifleman Well-Known Member

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    You might also try RL17. I believe they are advertizng it as stable at extreme temps.
     
  13. johnnyk

    johnnyk Well-Known Member

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    Vintec,

    This is the info that Hodgdon was putting out after the Extreme line came out.

    [​IMG]
    [​IMG]

    Hope you can read it....JohnnyK.
     
  14. vintec

    vintec Well-Known Member

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    Johnny,

    Is there a link to this info or is this a scanned image.

    Thanks

    Vince