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Barrel heat and velocity spreads.

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  • Barrel heat and velocity spreads.

    I was cleaning the reloading room and found some old paperwork from my .308 10FP savage heavy barrel testing.
    All shots in each of the groups were taken as quick as i could get the gun back on target, no rest between shots.

    First up was a starting temp of 87 F. ending at 95 F.
    First to last shot FPS.
    2540.
    2577.
    2583.
    2598.
    2609.
    69 FPS difference , discount shot one and it is 32 FPS difference.
    Cold clean oiled bore first shot made the group measure 1.860" discount that and the group was .695" center to center.

    Next up was starting temp of 99 F. end temp was 104 F.
    2599.
    2613.
    2608.
    2609.
    2613.
    Only 14 FPS difference. .928" group center to center.

    Final was 104 start and end temp.. seemed to not get much hotter as My notes state 104 end temp.
    2615.
    2628.
    2622.
    2611.
    2626.
    2645. This was seated long and into the lands.
    2604.
    Group size for 8 shots 1.185" One shot did not register on chrony.
    41 FPS spread or discount the one jammed in the lands it would be 24 FPS spread.

    That gun had a sweet spot at 95 -99 F and usually 4 shots would get me there then I could shoot and wait a minute or so and shoot again and it would print small patterns.
    The ammo was kept in the shade the entire time.. so this is not ammo heat soak from sun baking.

    Varget powder and 165gr bullet, lapua cases.



  • #2
    Thanks for developing and reporting the details of your tests. Always interesting. RD
    Every once in a while in life we need a policeman, a lawyer, a doctor and a preacher. We need a farmer three times a day, every day.

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    • #3
      Swamp I was wondering what tool did you use to measure the temperature? and at what point on the barrel did you take your measurements?
      I'm guessing the used one of the new more affordable laser pyrometers
      (translation digital thermometer point and shoot)
      The temperature ranges that you report had to be at the muzzle because it seems that the steel would get much hotter just forward of the chamber? Of course with a bull barrel they do take a lot longer to heat up
      so you got me wondering ?
      Salt&Light

      WOODSMAN777

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      • #4
        I used this
        https://www.summitracing.com/parts/WMR-W89720.
        Mother-in-law worked for parts plus auto parts and she got it from them..it was still 65 bucks back then.
        I compared it with my Fluke 87 multi meter with the Fluke temperature probe adapter..It was always within 5 degrees of it. Not too bad.

        I got it for Christmas about 7 years ago.. still works perfectly..I use it a lot to check header temp and tire temp and you can check hot spots in your floor for leaking hot water pipe under the slab.
        I check hot spot area's in the ceiling to see which area's need more insulation or possibly a reflective barrier.

        I checked the barrel about 10" in front of the chamber.

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