RL25 Temp experiment

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by DanMan, Feb 21, 2011.

  1. DanMan

    DanMan Well-Known Member

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    OK after reading several post about temp instability of RL25 I decided to do an experiment because thats what is my loads. I'm not worried about BR accuracy but sure dont want to miss a big bull while hunting in cold weather. I get 1/2 moa at normal temps. I chilled 6 rounds for 5 days @ 12F to compare MV to room temp loads. I set up my chrony so that I could fire within 60 seconds after taking the chilled load out of the refrigerator/freezer. I tested these in 3 groups of cold-warm-cold in each group. The ambient air and my rifle were 70F. These were my results:

    cold-3186, warm-3164, cold-3078 then wait 45 minutes
    cold-3167, warm-3183, cold-3128 then wait 45 minutes
    cold-3171, warm-3181, cold-3116

    I was happy with the 1st 2 shots of each round, what happened on the last shot each time?
    I noticed that in the few seconds it took to take the round out of the freezer and put it in my gun that frosty condensate would form on the brass. Do you think that on the 3rd shot of each round putting the cold load in the hot chamber condensation was forming resulting in the lower velocity?
    What do the experts think?
     
  2. nheninge

    nheninge Well-Known Member

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    100 fps difference over time could likely be chronograph error et al. Were conditions exactly the same over time? I also believe that an ambient gun temp with cold powder does not tell you much. So these "freezer tests" on powder are basically worthless. Actually shooting in cold air vs. cold round, warm gun is NOT the same. The starting temp of the powder does not matter much when it is heating to several thousand degrees. Temp effects on shooting are MUCH more than just a frozen cartridge. Granted you are just evaluating powder, but IMHO the only real way to test this is by actually shooting in different temperatures. This is no different than evaluating your rifles drop at different station pressures.
     

  3. DanMan

    DanMan Well-Known Member

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    Yes the conditions remained the same over the 2 hour period that this took. I do understand that ballistics change with air temp. and I can see where firing mechanism in a very cold gun could be slower, but if the starting temp of powder is not important then why do experts avoid "cooking their loads" in a hot chamber before firing?
     
  4. nheninge

    nheninge Well-Known Member

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    Starting temp is not as important as barrel temp. "Cooking the load" can cause barrel shift/warp. It is not that velocity changes as much as the barrel. Yes, velocity increases with barrel temp (powder temp). Most ballistics programs can compensate for this. If you zero in at 70 degrees and you are shooting at 40, you simply input the current powder temp. You can test your barrel by shooting multiple rounds while focusing at the same spot. As your barrel heats, impact will shift. This does not meas crap if you are a hunter that relies on an accurate, single cold bore shot. Much more important changes in environment, station pressure, humidity, wind, slope, quartering shot etc. than starting cartridge temp.

    Want to avoid missing that bull in cold temps??? Then you have to get out and shoot in EVERY condition possible from multiple positions. Doesn't matter if you can accurately predict your powder temperature velocity if you can't feel the trigger because your finger is frozen or you have buck fever! THIS training is very difficult especially with 8-5 jobs and hunting conditions that vary greatly from our practice conditions. It is VERY hard to be an accurate long range hunter without practicing in actual field conditions so..., keep your goals/distances realistic, focus on what you can control and realize that your ability to interpret field conditions will likely play more of a role in whether you kill or eat your tag.
     
  5. DanMan

    DanMan Well-Known Member

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    I think that the more tech stuff that I read the more anal I become.:)
    Thru the years I have taken bulls from 10 yrds to 650 yds in temps from single digits to one this year on 90 degree day, and mostly with factory guns and ammo.
    Used to always worry more about finding a good bull than being able to hit him.
    Just thought I'd do an experiment with my powder after reading a few post that suggested it might be temp unstable.