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More of an oddity than anything else, massive windage shift

Discussion in 'Rifle Country' started by Jenrick, Mar 13, 2019.

  1. Jenrick

    Jenrick Member

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    I was out shooting my FAL today, seeing what it liked ammo wise as I haven't put much through it. Fortunately it seems to really like Monarch 147gr from the local sporting good stores, which is about $8 a box. It groups quite nicely, with only minor windage and elevation differences compared to other brands I had on hand at 100 yds. When I backed up to 200 yds, it still grouped great. However it had a MASSIVE (about 8"-12") windage shift to the right. It was kind of surreal actually. I even tried loading up multiple brands of rounds in a magazine, just in case it was me, nope, still the big shift. I'm just curious why there'd be a 4-6 MOA shift at only 200 yds, and only with this brand of ammo. Any thoughts?
     
  2. rpenmanparker

    rpenmanparker Member

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    Well, first off the MOA shift is a relative measurement and should be constant at all distances, right? Just the absolute shift should respond to distance. So do you see half that shift in inches at 100 yards? If not, you have got something seriously screwy going on. If the MOA shift is indeed constant, 4-6 inches st 100 yards, 2-3 inches at 50 yards, etc., then no big deal. Just zero for the ammo and distance you plan to shoot.
     
  3. LoonWulf
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    LoonWulf Contributing Member

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    Only thing I can think of is sight alignment issues when you switched to the 200yd target. You are.perhaps seeing them slightly different, and that could cause you to shoot farther right.
    Unless the fall has a 200yd setting and your sights mechanically changed alignment when switching settings.
     
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  4. someguy2800

    someguy2800 Member

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    How hard was the wind blowing?
     
  5. Jenrick

    Jenrick Member

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    I'll take some pictures of the target tomorrow. Short version is that the round in question is probably maybe an inch off of the PoI of the rest of rounds (the scope is zero'd to a different round.) The other two rounds I was testing, showed the expected drop and minor shift from doubling distance. Then this round is way off. Wind was very minimal, less than 5 mph. I shot a couple groups with each brand 200 just in case it was me or environmentals. Nope it's the round some how.
     
  6. Skylerbone

    Skylerbone Member

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    Just a WAG as I’m not a ballistics kinda guy, but possible the bullet from that specific round is not completely settled yet? I used to shoot too light of spine weight arrows from my Howatt Hunter (~72 lbs @ 29 1/2”) and they would whip violently before the fletching could stabilize them.

    I do know from shooting rimfire that some ammo that looks great at 25 yards looks like scattergun patterns at 100 and some people no doubt won’t bother to check before heading afield. That can mean missed squirrels and head scratching later.
     
  7. illinoisburt

    illinoisburt Member

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    Doubt its a settling issue since its consistent. Very likely there is stress in the barrel around the gas block which is getting slightly different, but still consistent, harmonics from the other ammunition. Past online tests of the Russian rifle ammo in other calibers has shown very different pressure curves from US manufacture. It seemed like they often used a slightly smaller charge of a faster burning powder so the total pressure was similar but velocities tended to be less in long barrels compared to US loadings that had a longer pressure curve which spikes a little later.

    As for rimfire, that experience is very common with high velocity rounds. The bullets destabilize when dropping below speed of sound about 50-80 yards out (around 1125 depending on a bunch of factors). That's why good 22 target ammo is generally loaded in the 1050 to 1100 fps range.
     
  8. rpenmanparker

    rpenmanparker Member

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    But again, would you expect the destabilization due to dropping below supersonic to result in good groups? Wouldn’t the effect be fairly random? Or no?
     
  9. illinoisburt

    illinoisburt Member

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    Destabilization is exactly what the word means. The bullets wobble when the break under the speed of sounds. It's random and can throw the trajectory off course in most any direction resulting in very poor accuracy. Not to say it won't likely be close, just not exactly where it was expected (think bugeyes at 40 yards and 4 inches at 100 kind of stuff).

    Of course that really isnt the OPs issue. The rounds are grouping, they just moved off to one side versus a different loading. I'm betting on barrel harmonics being different. Wonder if a barrel weight or damper would alleviate it? Or maybe if $ didn't matter a cryo treatment?
     
  10. rpenmanparker

    rpenmanparker Member

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    Well that was the point I was trying to make. The destabilization from dropping below supersonic would yield poor precision.
     
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  11. adcoch1

    adcoch1 Member

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    What rear sight does your fal have on it? Or if this is ALL through a scope, what scope and mount do you have? Fal pattern rifles are notorious for poi shifts as they heat up, have you eliminated barrel heat up as a possibility? Also, shooting them off of a factory bipod instead of bags can heavily affect barrel harmonics in odd ways. Try bags and single shots from the iron sights for groups and see if the problems are lessened. An FAL has a lot going on per shot to mess up precise shooting.
     
  12. .308 Norma

    .308 Norma Member

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    Jenrick, it might be just my reading skills, but I've read your post several times, and I'm still confused. First you said you loaded "multiple brands of rounds in the magazine" and there was still a "big shift." Then you said "there'd be a 4-6 MOA shift at only 200yrds, and only with this brand of ammo."
    Which is it - multiple brands or one brand of ammo? Or am I just not understanding what I'm reading? Thanks.:)
     
  13. rpenmanparker

    rpenmanparker Member

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    I took it to mean that when different brands were mixed, he could see the difference. One type displayed the odd behavior even sandwiched between other brands of rounds that behaved normally. He kept track of which was which. At least that is my understanding.
     
  14. Varminterror

    Varminterror Member

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    Dude stuck rounds of a few different brands in a mag, knowing the order. Shot said mag. The one brand printed shots 4-6moa away from the rest of the impacts....
     
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  15. .308 Norma

    .308 Norma Member

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    Oh, okay. Thanks!:)
     
  16. Jenrick

    Jenrick Member

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    Mystery solved, it was an optics issue. Now the 30 MPH gusting wind this morning didn't help with solving this problem, but it was solved nonetheless. With irons, there was no lateral shift at all from 100 to 200 yds with this brand of ammunition. Now I'm curious WHY the scope and mount combo had this issue, but as this gun is going to at most get a red dot, and probably will live it's life as an iron sighted rifle, that's a back burner item for now.

    Also:

    Close I actually didn't know the order of the rounds. I loaded up the mag, set it aside, shot a few other things, and then came back to it to minimize as much of any bias/inconsistencies etc that I had. By that point I could see that the first round was brass cased, but beyond that I didn't have a clue what the next 19 in the mag where going to be.
     
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