By the numbers–Take two

If you have been following along in the comments at Say Uncle you will know that my assumptions about the cartridge used in my simulation here were off a bit. I assumed a 300 grain bullet with a BC of 0.785 and a MV of 2750 fps. According to Mu the correct bullet is a 250 grain leaving the muzzle at 3070 fps with (according to SteveA) a BC of 0.587. This changes things some.

The sight angle for no hold-over is 127.8 MOA instead of 122 MOA.

The time of flight is 5.2 S instead of 4.9 S.

The velocity of the bullet at the target is about 924 fps instead of 1043 fps. This results in PF of 231 instead of 313.

The number three shot groups required to get one that was less than or equal to 1 MOA is, on the average, 4.3 instead of 4.9 (initally my program showed 83 but now it shows 4.9, I suspect some sort a caching error in Modern Ballistics). But those numbers are identical given the margins of error used in the assumptions that generated them.

Both Modern Ballistics data files for the simulations are here.

See also the comments at Tam’s.

3 thoughts on “By the numbers–Take two

  1. Is this taking the elevation into account? I’ve heard these REALLY long shots being made in Afghanistan are being helped by the fact that the air is so thin at altitude.

  2. Joe, I ran the numbers, and based on the equipment used came up with a different conclusion.

    250 gr Lapua Lockbase bullet (G1 BC 0.662) mv 3071 fps. Schmidt and Bender PMII optic with 56 MOA of vertical up from zero. A quoted holdover of “about six feet”.

    Based on my assumption of 5,000 feet above sea level the maximum distance that 60 MOA of drop with that load is right at 1750 meters, or just over one mile. If the angle of the shot was 45 degress then it all adds up. 2474 meters times cosign45 degrees equals 1749 meters.

    Considering that put CPL Harrison 1749 meters vertical AND horizontal distance away from his targets, it still adds up to amazing shooting.

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