Retumbo in cold weather? My rifles suddenly started shooting Low.

Discussion in 'Reloading' started by Roll-Yur-Own, Dec 10, 2006.

  1. Roll-Yur-Own

    Roll-Yur-Own Well-Known Member

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    I shoot 7 RUM and 338 Lapua both with retumbo loads. The weather here got real cold and the load are suddenly shooting significantly lower. Has anyone had this problem with retumbo?
     
  2. Michael Eichele

    Michael Eichele Well-Known Member

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    At what range?? At your zero or at some distance beyond your zero?
     

  3. wapiti13

    wapiti13 Well-Known Member

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    Roll-Your-Own, Velocity has probably dropped off with the cold. Less velocity, more drop. Even extreme powders are not totally stable with temperature changes. Are you using a magnum primer? I assume so, but magnum primers help as the temp drops. /ubbthreads/images/graemlins/confused.gif
     
  4. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Roll-Yur-Own,

    There is no way to get a load that shoots the same in warm and cold weather. In my experience, the larger the case capacity and the smaller the bore, the more variation you will see as far as bullet drop changes in different temps. This will happen with any powder, yes some powders will be better then others at limiting velocity change in different temps but I would say your using one of the better powders already.

    Only way to know is to shoot in these different conditions and make notes of it. The main problem is that most will develope a load in the summer time when the temps are warm and then shoot all summer, this is great and what you should do, only problem is that when hunting conditions show up with cooler temps, the rifle should really be tweaked to those conditions.

    Best time for load development in my opinion are spring and fall when temps will be similiar to what you will be seeing in hunting season. This is of course for a big game rifle.

    For long range varmint rifles, I recommend developing loads in the heat of the summer if that is when you will be using them to make sure they will be safe in all temps.

    Simply put, welcome to the game, unless your seeing several feet of drop difference, you are not seeing anything unusual even with Retumbo.

    Kirby Allen(50)
     
  5. Roll-Yur-Own

    Roll-Yur-Own Well-Known Member

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    I shooting a load 2" high at 100 yard with my RUM. I shot a deer with it on November 19. Now the same rifle is about 10" low inside 100 yards.

    Similar results with Lapua. That seems a little odd.
     
  6. papa45

    papa45 Well-Known Member

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    A 12" drop? That's not your powder.
     
  7. Roll-Yur-Own

    Roll-Yur-Own Well-Known Member

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    On 2 different guns?
     
  8. royinidaho

    royinidaho Writers Guild

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    Yup - I tend to agree w/papa45. Wholly cow, 12" of drop @ 100 yds sure should be entirely attributed to velocity loss. Though I haven't run the numbers the vel. loss would have to be in the thousands of FPS not 100s.

    In a 270 Win w/RL-22 and 140 Hornadays @ 3190 or so in the summer drop to 3060 or so in the winter and don't make much of a difference at all at 200 yds but down range a ways it rears its ugly head.

    It will be interesting to learn of your conclusions.
     
  9. MagMan

    MagMan Well-Known Member

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    Would it be possible you are 1 full rotation off on your dial?

    I just did some rough figuring for 7mm RUM and what you are talking about would be a 1500-1650 fps drop depending on bullet weight. I also think you have far worse problems than Retumbo temp sensitivity (or appearance of such sensitivity). I only lost 65 fps going from 90 deg. to 35 deg. using Retumbo in 7mm RUM.
     
  10. remingtonman_25_06

    remingtonman_25_06 Well-Known Member

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    Scope coulda got knocked off while transporting, shooting, or hunting. I've had that happen to me several times. I always try to be extra extra careful when handling guns. I dont like banged up scopes or rifles. Just a thought.
     
  11. Chawlston

    Chawlston Guest

    Did you use a mirage shade when you originally did the load work ups in the warmer temps. If not, you could easily see what you are getting in both guns with different scopes. This happened to me and I started shooting 12" low at my zero. Once I started using a mirage shade, the problems ceased to be evident. Also, pilot error could be one of the causes.

    James
     
  12. coupalr

    coupalr Well-Known Member

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    I have been shooting Retumbo in my 7STW and I have observed about a 12" difference in drop do to temp change this winter. This is at 723 yards though and the temp. difference is ~ 30 Celcius.
     
  13. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Thats a mechanical issue I would bet, either scope got bumped or something shifted with the stock.

    May just be a simple scope bump and you need to rezero.

    From hot to cold temps you should see very little point of impact shift if your only shooting at 100 yards. I was referring to long range that you will see a bullet drop going from hot to cold temps.

    Rezero your rifle and see what it does with a proper +2" at 100 yard sight in.

    Kirby Allen(50)
     
  14. Roll-Yur-Own

    Roll-Yur-Own Well-Known Member

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    It may just be coincidence that it happened to 2 rifles?