Powder Temp.

Discussion in 'Long Range Hunting & Shooting' started by louis f, Aug 11, 2018.

  1. louis f

    louis f Active Member

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    Dose anyone know what happens with velocity of a cartridge, when the ambient changes. What I am looking for. If the velocity change is lets say, 100 fps form 0 degs. to 125 degs. And at 62.5 degs. you have x velocity. Will you lose more velocity,(Total fps) going down to 0 degs. Or will you gain more velocity ( Total fps) going up to 100 degs. In other words what makes the bigger difference in the total velocity change. Which has the biggest difference Up or down???
     
  2. dok7mm

    dok7mm Well-Known Member

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    Run your load thru JBM ballistics free solver. You can play with temperature and/ or elevation, to get a close idea of what you're looking for. The Hodgdon Extreme powders generally have less temperature influence on velocity.

    To know exactly what a given load will do in your rifle, you can either freeze or heat ammo and shoot over a quality chrongraph. You can control the temperature of your ammo and, to an extent, your rifle.
     
  3. predator 22

    predator 22 Well-Known Member

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    There is no set value as all powders are different and the degree of change isn't the same between different cartridges. Best to test your combination with a chronograph.
     
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  4. FlGunner

    FlGunner Well-Known Member

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    I've seen the guys on Gunwerks do an example on youtube shooting ammo that had been left in a cooler versus ammo that was as same as the outside temp. I believe they were using Retumbo in a 7mm Remington mag but I might be wrong on the caliber. Anyways there was some difference but nothing drastic. I believe all powder is sensitive to some degree and that a particular powder may be better suited to a specific bullet in your particular gun to where it isn't effected as say a different powder. I shoot H1000 in one 7mm Remington Mag and Retumbo in another. Both have low ES/SD. My sendero loved H1000 and the SPS loves Retumbo. Neither do as good with the other powder. I too tried freezing a few rounds and shooting them and didn't see much difference from ammo at ambient temps. I think air density, humidity, and elevation all play a part in the relationship to velocity and temp stability as well. Hopefully some of the more experienced guys will chime in. I hope I ain't completely wrong lol, just what I've seen with my shooting here in FL. I can say that load work up I done in the summer with high humidity had no real change in December and January when we see lows in the 30's and low humidity.
     
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  5. Schnyd112

    Schnyd112 Well-Known Member

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    You just have to try it. I haven’t seen anything consistent enough to give you advice because all of my loads have handled it differently. Today it got hot and things started running away on me. I haven’t shot this load much so I was guessing on my corrections. Made for a tough second half of the match.

    My takeaway from shooting a competition in sunny 100 today: it’s great when you can put your gun in the truck, or under the truck in the shade, during practice to cool it off but I don’t think it does any good for competition. I suspect today that it was more the ambient heat of the gun than the ammo or the air.
     
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  6. woodnut

    woodnut Well-Known Member

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    Don't know if this helps or not, but I just ran a load at 74 degrees and again at 90 degrees. With RL19 and 105s in a 6 Creedmore, I gained 90 fps at 90 degrees. Odd,huh? Could not, however, see any more pressure signs than I did at 74 degrees; which was nothing. Other times, a load in a different cartridge was a radical difference! Pressures much higher, but I also will say that load was already pretty hot. So, remember what others have said, no set values and try the JBM ballistics solver. And be careful!
     
  7. Canhunter35

    Canhunter35 Well-Known Member

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    I’ve seen extreme cold affect varget and h4350 by dropping velocity by 150fps on well developed loads. That was around -35degrees. I’ve read in extreme heat it can also do the same thing. Down to -25degrees the powder remained consistent enough I never worried about the fluctuation
     
  8. Wedgy

    Wedgy Well-Known Member

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    This is only my experience from out West where it gets over 100F for a couple months and rarely gets below freezing. I see very little rise in velocity with temperature, usually 0.5 to 1.0 fps per degree F from ~50F until about 84F, then the velocity will start to pick up much more per degree of F increase, some up to 2 fps per degree. At that point it is not a powder I can use because if I test it at the higher temp it loses so much velocity at the lower temp it's not in the node I tuned for. It can easily be close to freezing in the morning and near 100F during the day, very low humidity but I don't think that affects the burn inside the case. For me Reloder 26, 33 have shown huge increases over ~84F and I have had very good success with H4350, Varget, H1000, & Retumbo, As well as N570 but I can't find it anymore. Again, I only have to deal with the upper ends of the temperature swings.....hot flashed if you will.
     
  9. predator 22

    predator 22 Well-Known Member

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    Did you happen to test different primers to see if it was the powder or primer causing the problem?
     
  10. Canhunter35

    Canhunter35 Well-Known Member

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    I never tested primers but both loads used 210s so that could be the common denominator, or it could very well be both. It’s so frickin cold at those temps, after I shot below my 3rd coyote I went to my 1/2mile gong and dialed till I was on it, coming up with -150fps. I accounted for air density(I think -1500density alititude) at -25 my dope was on but somewhere colder than that things changed
     
    Last edited: Aug 17, 2018
  11. louis f

    louis f Active Member

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    After some more load and range work, IMR 4831 powder seems to really pick up velocity after 70 degs. Trying to figure out the powder temp. and fps change for my shooters app. 1.5 degs. worked well from 54 deg powder temp up to about 70 degs. After that the fps of change per deg. was to great. An Antelope hunt this year in Wyoming the end of sept. Temps can be all over the board. I have shot H-4831 but don't get the accuracy. I have settled on just changing the velocity part of the app. as best I can, based on proven temp. and velocity readings.
     
  12. Wedgy

    Wedgy Well-Known Member

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    I have heard Reloder 16 is very stable and similar to H4350 but have not tested it as I am happy with H4350 and it is available....for now.