Breaking in 300 win mag

Discussion in 'Reloading' started by PDA, Oct 8, 2009.

  1. PDA

    PDA Well-Known Member

    Apr 7, 2009
    Put a new barrel on my old 300 win mag Sendaro, stayed with same round because I am set up for it and it just works for me. Brux barrel, 27" finished, JP tactical brake. Gunsmith work done by Scott King in Cashmere. He had done a few buddies rifles and seems to know what he is doing.

    Spent today breaking in the barrel. ALL DAY shooting and cleaning. Tested a few loads and here is what I found. All loads with 208 gr A-max at 100 yds

    My old load for this rifle, bullet seated farther back to account for the shorter throat, .005 off the lands.

    68 gr IMR 4350 fed 215M Primer Ave 3046 fps ES 113! (over 20 rounds)

    3 shot groups of .26, .375, .45
    5 shot groups of .75, .52, .62

    New loads

    76.6 gr H1000 Fed 215M primer Ave 2931 fps ES 67 Accuracy 3 -.65" / 5 - 1.35"

    76.8 gr H1000 Fed 215M primer Ave 2929 fps ES 42 Accuracy 3 - .43" / 5 - 1.59*
    ( 4-.53" CB was way off)

    77 gr H1000 Fed 215M primer Accuracy 3 - .63" / 5- 1.68"

    77.2gr H1000 Fed 215M primer Accuracy 3 - .55" / 5 -1.10"

    77.4gr H1000 Fed 215M primer Ave 2954 fps ES 20 Accuracy 3 - .4" / 5 - .85"

    No pressure signs yet. I am perplexed by the ES of the IMR4350, all charges were weighed individualy. Will try CCI 250 primers with the same load next. Also going to try increasing charges of H1000 in .2 gr increments with both F215M and CCI250 primers. Groups seem to be shrinking as charge weight increases with H1000, hoping to get better groups and better ES. I have heard that H1000 is much less temp sensitive than IMR4350. Any input guys?
    Last edited: Oct 8, 2009
  2. J E Custom

    J E Custom Well-Known Member

    Jul 29, 2004
    The 215s may be to hot for the 300WM and I would recomend trying a 9 1/2 m Remington
    primer or even a standard large rifle primer.

    I have had the same thing happen to me with cases that hold 70 to 80 grains of powder .

    They were faster with the 215s but the SDs were poor so I tried the 9 1/2 Ms and lost a
    little velocity but reduced the standard deviation's by almost half.

    The bigger cases (100+) grains of capacity do better with the 215 or 215ms.

    Also H 4831sc is a great powder for the 300 WM.