AR technique? - accuracy from the bench

Discussion in 'AR15/10 Rifles' started by jtbiv01, Sep 30, 2018.

  1. jtbiv01

    jtbiv01 Well-Known Member

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    .223
    good barrel - Shilen
    Light trigger - timney
    Stag upper
    Multiple factory and hand load combinations.

    Can’t get it to shoot.

    Any recommendations on shooting from the bench techniques? I’d buy a different bag or rest to keep from scrapping the rifle. I shoot my bolt guns just fine. This gasser is killing me.
     
  2. ShtrRdy

    ShtrRdy Well-Known Member

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    Is there any looseness between the upper and lower?

    It's been awhile since I shot my AR for groups but it seems like I had the best result by pulling the rifle into my shoulder such that the upper was preloaded into the lower.
     
  3. jtbiv01

    jtbiv01 Well-Known Member

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    Have run a yellow ear plug and now an accuwedge between the u/l. It’s tight. Rear stock is magpul ACS-L. This one is baffling me.

    Thanks for the response!
     
  4. ShtrRdy

    ShtrRdy Well-Known Member

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    Can you trust the optic and mount?

    What size groups are you getting?
     
  5. jtbiv01

    jtbiv01 Well-Known Member

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    Scope and mount are sound I think. American Defense mount. 2-3 different scopes while I was trying to find what I like. VX-6 2-12x on it right now.
    1.5”-2” groups with handloads that shoot .5” in my cuz 527. 55gr Ballistic tips


    Tried black hills factory, hornady, federal premium, hsm, and Winchester. Different weights and types.
     
  6. LaHunter

    LaHunter Well-Known Member

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    I don't shoot my AR as well as I shoot my M700 7mm rem mag. I put a fair amount of pressure into my stock and really get my check weld firmly in place when I shoot my bolt rifle. I also 'load' my bipod with my bolt rifle. This seems to hurt my accuracy with my AR. I seem to get better groups with my AR when I use minimal pressure on the stock and I don't really load the bipod much at all. It's definitely a different technique from shooting a magnum bolt rifle.
     
  7. jtbiv01

    jtbiv01 Well-Known Member

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    Thanks for the reply
     
  8. 300whisper

    300whisper Well-Known Member

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    What’s the barrel length and twist? Also, the gas tube length? I know 55 grain and below start shooting poorly in a fast twist, long barrel. The gas block length is something my smith told me, but I can’t comment on how that would affect accuracy.

    My shilen barreled AR really starts shining in the 68-77 grain realm. It’s 20 inch, heavy contour, 1:7 twist. Mine shoots the 55 grainers right around a MOA to 1.25 MOA for 5 shot groups.

    Edit: sorry just saw the “tried the multiple load combinations.”

    Maybe something different with recoil impulse? I know friends who jump when the buffer tube assembly is recoiling. You feel that springy sensation in your cheek.
     
    Last edited: Oct 1, 2018
  9. cohunt

    cohunt Well-Known Member

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    Is it overgassed? Over gassed rifles mess with the accuracy as they try to extract the brass while the bullet is still in the barrel
     
  10. 300whisper

    300whisper Well-Known Member

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    Is that what is meant by running the right gas block / length?
     
  11. cohunt

    cohunt Well-Known Member

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    Most ar's come overgassed (larger gas port than is necessary) for reliability in any condition with any ammo (including underpowered factory ammo)

    A properly gassed ar should eject the brass cases from 3:30- 4:30 o'clock position--- if the brass is going 90° to the side or forward of that then it may be overgassed and need an adjustable gas block--- you can band-aid it by using a heavier buffer but that wont fix the overgassed problem, just slow down the rearward momentum of the carrier.

    Your gas tube length will be dictated by the location of the has port on the barrel -- pistol, carbine, mid, rifle, &extended (extended systems are usually proprietary to the manufacture)

    Any gas block can be used, as long as the ID is the same as the OD of the barrel journal

    Adjustable gas blocks can be adjusted from full open, to full closed to regulate the amount of gas exerted on the gas system.

    Any buffer/stock can be used as long as the componants match - ex: rifle buffer must be used with rifle buffer tube and spring & carbine buffer must be used with carbine tube and spring BUT you don't have to use a rifle buffer system with rifle length gas system as they operate independently of the other (but in conjunction)

    Short ar barrels on light ar's will compound accuracy issues due to muzzle jump-- I have a 308w AR that weighs about 6.5 pounds with optics-- it takes quite a bit to manage the muzzle jump and get the gas fine tuned for accuracy

    Also make sure the barrel is not copper fouled, people tend to shoot more rounds than they realize through an ar and often times the barrels are copper fouled.
     
    just country and 300whisper like this.
  12. jtbiv01

    jtbiv01 Well-Known Member

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    I haven't thought about the over-gas situation. If I remember correctly, it's ejecting over my shoulder. I've got a mid-length gas tube.

    Just to confirm, if ejecting to the front or directly perpendicular to the ejection port - try and adjustable gas block?

    The barrel is 20" - don't know if that affects gas pressures...
     
  13. cohunt

    cohunt Well-Known Member

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    Technically gas pressure isn't actually the issue it's related to boyles law of how much pressure and how much volume of that pressure over what amount of time. It's related to the energy required to move the bolt carrier group.

    Your barrel (no matter what overall length or gas length it is) has a hole drilled in it...on longer gas systems the hole has to be larger due to lower pressure at the port ( less pressure means more volume is needed) - pretty much this is fixed by the manufacture ( though you can drill it larger if more gas is needed) --- most manufacturers drill them larger than needed so it will function even with "light" loads.

    In order to reduce too much pressure/volume you need an adjustable gas block so you can "cover" part of an oversize gas port.

    If its ejecting over you shoulder it's probably fine as that's where it should be. Are you running a carbine buffer system or rifle buffer system?

    If you want to do a cheap test to see if the gas is affecting your accuracy then if the gas block is not pinned (either set screw or clamp style) then slide the gas block forward about the thickness of a nickel and then shoot ( it wont be semi auto as it will block the gas going back to the carrier) ...if it's more accurate this way then it's most likely over gassed and you need an adjustable gas block.

    Did you check for copper fouling in the barrel? Did you take off the muzzle device and check the muzzle crown for nicks or damage?
     
  14. Johnny_V

    Johnny_V Active Member

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    I've had problems with my AR from the bench until I hit upon the right load. I'm shooting a 1 in 7 barrel with 77gr SMK in front of 22gr of IMR4895 (this is my load and take no responsibility for its validity in anyone else's rifle) and get really respectable groups.
    MK12.jpg
     
    Dave in WI likes this.