windage shift in factory ammo

Discussion in 'Rifle Country' started by mucko, Nov 1, 2020.

  1. mucko

    mucko Member

    Nov 1, 2020
    Hey Team first post here from New Zealand, just got back from the range with my ruger mk ll in 300wsm, it was a healthy recoil before fitting a schultz and larsen suppressor, i test fired federal 165gr .5" low at 50yds and norma 180gr .5" low at 50yds the norma grouped the tightest but was 2" right of the federal. anyone have any idea why?? cheers
    Demi-human likes this.
  2. Demi-human

    Demi-human Member

    Dec 8, 2016
    The Haymarsh, MI ( Aka, Paradise.)
    Firstly, welcome to the forum, from literally the other side of the world!:)

    Barrel harmonics and two different loads.

    The waves of energy that cause the barrel to undulate when fired do so in a round fashion, not just up and down. When the bullets of one load leave the barrel they do it in a section of time that the barrel is pointed to the right. The 180’s take longer to exit the barrel.
    A charge of different powder can have the same bullets leave at a different point in the wave cycle of the barrel.

    The waves can reverberate from breech to muzzle around 18 times before the bullet leaves the barrel in a 20” .223.
    gspn, Ru4real and wiscoaster like this.
  3. edwardware

    edwardware Member

    Feb 23, 2010
    @Demi-human has it right. I can add from experience that increasing charge weight often shifts groups up and right (I'm right handed, shooting bagged on a bench), sometimes rightward much more than upward.

    This can be true across recoil levels (.222 to .375) and platforms (bolt guns to ARs). You and the gun are a mechanical system, and recoil is more than just "up".

    If you haven't already, look up Nathan Foster, a fellow New Zealader. His books have been quite valuable in my rifle skills development.
  4. Archie

    Archie Member

    Dec 31, 2002
    Hastings, Nebraska - the Heartland!
    I've had similar problems with rifles. Not sure I have an answer that fits all questions, but have a couple ideas to check.

    As mentioned already, loads from differing sources will print to different points of impact. The type of powder used the type of bullet used, the type of arm will all react to each other to shift windage. No idea of how to predict this.
    Presuming you are using factory ammunition: If groups are acceptable and fairly round, adjust the sights and stick to the load that works. Don't buy 'anything' and expect it to all work the same. Next season you may have to find another factory load, as factory ammunition may (or may not) change powder, charge levels (to get same velocity) or different types or lots (batches) of bullets - all of which can change the 'balance' of a load. When one finds a load giving good results, buy as much of that 'lot' of ammo as possible.

    If using reloaded ammunition, the situation is similar, but one should think of the same sorts of factors as applicable to ones situation and control.

    One rifle I can (a .22 long rifle) would change windage strike with range adjustments. Turns out the scope was mounted with the axis of the scope just slightly out of line with the axis of the rifle bore. (They weren't 'looking' the exact same direction.) Just a thought, but if that rings a bell, check it out. If nothing else seems to help, check it out.
  5. jmr40

    jmr40 Member

    May 26, 2007
    Having one load shoot a bit left or right compared to another load isn't unusual. But 2" at 50 yards is pretty extreme. Never seen anything that far off.
    Demi-human likes this.
  6. wiscoaster

    wiscoaster Member

    Sep 19, 2019
    Nice explanation. :thumbup:
    Demi-human likes this.
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