308 Rem 700, chasing numbers on the chrono

Steven308

Private
Minuteman
Sep 23, 2021
18
6
Foreston MN
Working on a load for my 308, here's what I've got-
Remington 700 with a 26 inch heavy barrel in a Manners T4A stock
Competition Electronics Pro Chrono
IMR 4064
CCI NO. 200
Hornady 168gr BTHP match
Lapua brass

I've shot multiple groups going from 40.5 grains to 44.5 in .3 grain intervals (using Nosler and Lyman books), and so far I get the best group with 43.9 grains and a COAL of 2.810. If I were to have the bullet touching the lands, my COAL would be a ridiculous 2.9525 inches which is way beyond my magazine length (is this a fluke!?). I tried loading some at max magazine length but wasn't getting as good of results, but that could be due to other factors. Anyway, my first 3 round group of 43.9 at 100 yards measured .21 inches, with an ES of 40 and a SD of 18, average velocity 2762fps. The chrono was 10 feet away from muzzle and my readings were jumping around a lot with all loads that day (and in the past with other rifles and loads using the chrono at that distance). I should note all loads were loaded within .05 grain. Since I liked the group size I decided to redo that load, putting the chrono 15 feet away on a hunch just for shits and giggles to see if it made a difference. This time, 10 shot group size of .8 inches with an ES of 34 and SD of 11, average velocity 2741fps. Am I crazy for thinking moving the chrono back that far is avoiding some random muzzle interference therefore giving the more consistent numbers? I like the groups I'm getting with this load but I don't like the numbers for fear of the vertical spread I'll get out past 6-700 yards.
Should I be using a different chrono? Using the chrono at a different distance from muzzle? Different seating depth? These materials are what I bought a lot of so it's kind of what I'm stuck with, although I do have a handful of Federal Gold Medal Match 210M primers for my 300 win mag I could try if all else fails. I've been full length sizing, do I need to neck size only? What do you guys consider acceptable numbers (ES and SD) for 1 MOA accuracy at long range? Not sure what direction I want to go with my next round of tests, and heard some great things about this forum so I thought I'd give it a try. Thank you for the opportunity to share, looking forward to growing in my knowledge and skill.

Steven
 

Mike Casselton

Non-Bidenary Trunk Monkey
Full Member
Minuteman
  • Nov 25, 2007
    7,842
    12,432
    Lithia, FL
    When using an optical chronograph, make sure you have it set up where the bullets pass directly over the "eyes".

    Also, the closer you get to the eyes, the better your data will be.

    The issue with being too close is the possibility of turning your chrono into a pile of useless electronics.
    Just be careful and get it set up correctly and your data will improve.

    And yeah, at least ten feet away, fifteen is best.
     

    Doom

    Balding Eagle
    Full Member
    Minuteman
    Mar 24, 2013
    560
    288
    South of the Mason Dixon Line.
    10 ft is too close for a 308 to get good reading.

    A few comments on your load.

    43.9 may be a node as I have found it with the SMK but it’s not wide. The best loads are around 43 grs. I’m slightly over that with Lapua brass.

    Your statistics are good for a 10 round sample. You are loading consistent ammo. Let the targets determine whether your load works.

    You have discovered that Rem 700 308’s have what could be called a generous freebore. You can load out to about 2.850 COAL but staying around 2.800 should work out fine.
     
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    bluejay75

    PX Ranger
    Minuteman
    Aug 23, 2021
    81
    29
    North Carolina
    I found that I could never get below 8 SDs with 155s or 168s. But it sure did group nice. Here is what my 700 20 incher does with 168 Speer Gold Dots. I’m a hunter first so I can live with a 10 SD. But for 175,178 and 180s I find I shoot 0-2 SDs most times with well developed loads. I think it’s the nature of the powder.

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