Does extreme temperature changes affect bullet accuracy?

Discussion in 'Reloading' started by 300WineMag, Feb 11, 2014.

  1. 300WineMag

    300WineMag Active Member

    Messages:
    32
    Joined:
    Feb 14, 2012
    Been reloading for only two years and looking for comments from others with more experience. This summer I dialed in two rifles, FN SPR in 308 and Blaser R93 in 6.5 x 284. I keep reloaded ammo in an insulated cooler so the ammo doesn't get too hot sitting in car, but I am sure it still gets hot. This winter in Michigan the temps were quite cold. I shoot a lot at an indoor 200 yd range with no wind to deal with. The 308 used IMR 4064 and the 6.5 used H4831sc. Primers are CCI 200, flash holes deburred, full length resizing, accurate COAL, same powder weighed accurately.

    Both guns when zeroed at 200 yds at 70-90 degrees shot 2-3" low at 200 yds at 20 degrees. Never checked speeds with crono but both guns are sub .5 MOA. I guess the guns also have those temperature swings too now that I think of it.

    Has anyone else seen that much shot placement variation due to temperature of ammo? I had dope worked out to 700 yards for both guns in warm weather and had to redo it for cold, is that normal?

    Thanks for the help!
     
  2. Team Roper

    Team Roper Well-Known Member

    Messages:
    136
    Joined:
    Feb 10, 2009
    This is why it is so important to use temp stable powder. You problem is not an accuracy problem but a point of impact problem if I read this correctly. Yes this is normal with loads worked up not using temp stable powder.
     
  3. Mark611

    Mark611 Well-Known Member

    Messages:
    56
    Joined:
    Jun 13, 2012
    yes it will! even with temp stable powers you can lose as much as 100fps from hot to really cold conditions! that's what I see from summer temps to winter temps across my chrony, gun)
     
  4. 300WineMag

    300WineMag Active Member

    Messages:
    32
    Joined:
    Feb 14, 2012
    Yes it was point of impact much more than accuracy that was affected. I had read something about federal primers solving temperature related issues, but thought the 4064 and 4831sc powders were popular enough that they wouldn't be temp sensitive. Should research and test some others I guess - any recommendations for less temp sensitive powders?

    Also as I worked the loads up I stopped when I hit accurate loads so my weights are in the mid range, not on the high end of powder weights. Any thoughts if more air space in the casing exaggerates the problem or not?
     
  5. Mark611

    Mark611 Well-Known Member

    Messages:
    56
    Joined:
    Jun 13, 2012
    I would look into the Hodgdon Extreme powder line that's what I use:D
     
  6. Canadian Bushman

    Canadian Bushman Well-Known Member

    Messages:
    1,674
    Joined:
    Jan 24, 2012
    All powders are affected by temperature some just less than others. Bullet flight is also affected by temperature. Cool dry air is much more dense than hot moist air. Bullets impacting low on cold days is something a shooter will deal with regardless of what powder he chooses.
     
  7. Mark611

    Mark611 Well-Known Member

    Messages:
    56
    Joined:
    Jun 13, 2012
    I agree 100% it doesn't matter what you use you will need to learn what it does in all conditions, temperature and the elements changes everythinggun)
     
  8. CB11WYO

    CB11WYO Well-Known Member

    Messages:
    554
    Joined:
    Nov 13, 2012
    yup yup... +1
     
  9. LaHunter

    LaHunter Well-Known Member

    Messages:
    314
    Joined:
    Sep 30, 2012
    I would also say yes that temperature can and will impact mv / pressure. I have seen a 50 fps increase with a 30 degree increase in outside temps, based on my chrono. I use IMR 4350 in my 7 mm mag loads.
    I have not been reloading for real long, but most info that I have read leads me to believe that all powders are temps sensitive. Some are just more temp sensitive than other.