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AR 1/9 twist vs 1/7 twist...?

Discussion in 'Rifle Country' started by 61chalk, Mar 21, 2010.

  1. 61chalk

    61chalk Member

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    I've been shooting my Colt AR-15 for some time with a 20" HBAR
    1/9 twist. My son just bought a used Colt AR complete upper, 20"
    HBAR with 1/7 twist for 300.00 at a local gun show an then bought
    a new complete lower, folding stock DPMS for 199.00..we were wondering
    what some of the pro an cons are...seems I read awhile back that the 1/7
    twist has better performance with heavier bullets..?
    Looking for some knowledge from you guys....thanks.
     
  2. Shung

    Shung Senior Member

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    yes, that is it.. with the 1/7 you can go up to nearly 80grains...

    I suspect that the limit for the 1/9 is around 69grains..

    On the other hand, you can shoot lighter bullets with the 1/9.. maybe down to 52 or 55 grains..
     
  3. HOLY DIVER

    HOLY DIVER Senior Member

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    most 1/7 will shoot 55gr maybee not sub moa
     
  4. DMK

    DMK Senior Member

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    I shoot 55gr in my 1/7 twist AR15s all the time. I can't tell any difference in accuracy between them and the 1/9s.
     
  5. Zerodefect

    Zerodefect Senior Member

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    1/7= 62 and up to 77 OTM, 55 is ok at 100 yards but gets weird after that sometimes.

    1/9= 62 and less

    1/12= never shot one, suposed to be a 24" varmit barrel I guess.



    I prefere 1/7 so I can plink with 55gn and up and keep mags of 70+gn OTM's for defense or long range target shooting. SSA has some nice ammo.
     
  6. jaholder1971

    jaholder1971 Senior Member

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    1/7 will shoot any bullet that can be loaded to fit the magazine. Literally billions of rounds of M193 have been fired in training by our servicemen using M16A2 rifles (1/7 barrels) out to 300 and in the case of the Marines to 500 meters with few issues.

    I've never seen any major issues with shooting light bullets in fast twist barrels. The barrel twist isn't optimal but will still be accurate. The same cannot be said of a heavy bullet in a slow twist barrel.

    I have seen some of the really thin jacketed bullets designed for the .22 Hornet some apart in flight, but any bullet you'd use in a .22/250 should work fine in a fast twist .223 barrel.
     
  7. briansmithwins

    briansmithwins Senior Member

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    My 20" 1/7 light weight will shoot1.2MOA groups with PPU 75gr. With PPU 55gr it opens up to 1.8~2MOA.

    1/7 ain't optimal for 55gr but it ain't a horrible choice either. BSW
     
  8. briansmithwins

    briansmithwins Senior Member

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    Doublepost doubleplus ungood!

    BSW
     
    Last edited: Mar 21, 2010
  9. amd6547

    amd6547 Senior Member

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    1/12 was standard on the VN-era M16A1. My retro A1 based on a GI upper is very accurate with 55gn M193 and lighter. Good with 62gn,too. My 1/9 carbine upper does OK with 55gn.
     
  10. Al LaVodka

    Al LaVodka member

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    Faster twist, heavier. There are some odd defenders of the AR out here sometimes but my rule of thumb is that I won't bother using a 55 gr. in 1/7 (which were, in fact, designed for heavier NATO 62 to 77 grain rounds) nor bother shooting 62's in a 1/12. 1/9 is probably most accomodating. I'd even settle for a 1/8. If you have a 1/7, just accept that you CAN use 55's, yes they'll work, but you're really going to be relegated to 60+ grain bullet-spitting. I personally happen to prefer the 62's anyway...
    Al
     
    Last edited: Mar 21, 2010
  11. mshootnit

    mshootnit Senior Member

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    1/9 twist is better for the sportsman period. Seen any commercial loads for weekend shooting or hunting with bullets heavier than 72 grain lately?
    BTW my 1/12 twist bolt 223 stabilizes a 62 grain bullet just fine.
     
  12. wanderinwalker

    wanderinwalker Senior Member

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    In this case, IMO, bullet quality matters more than barrel twist. Realistically, 55gr M193 just isn't all that great in an accuracy match against, say, a 52gr Sierra Matchking load.

    I happen to use a 1-7" twist on my Service Rifle AR. It will shoot 52gr pills into tiny knots (MOA or less) at 100-yards. It will shoot 80gr slugs into useful groups at 600 yards. And it will shoot 55gr FMJ too, but I haven't bothered waste good match-barrel life on surplus. The old barrel was a 1-8", and I did shoot some 55gr FMJ in it, with useable accuracy, but definitely not up to the consistency of the 52gr match loads.

    I say we'd be better of not worrying about barrel twist so much and just shooting the things! ;)
     
  13. Lloyd Smale

    Lloyd Smale Senior Member

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    ive got both 1-7 and 1-9 guns and ill take the middle ground and if i was going to build one from scratch id probably go 1-8
     
  14. dom1104

    dom1104 Senior Member

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    something else to think about, 1/9 is a little easier on your 22lr conversion kit.

    I have not had any issues shooting 55 gr out of my 1/7 or 69 grain out of my 1/9.

    Never found any higher than 69 grain bullets so I cant help ya there.
     
  15. EdLaver

    EdLaver Senior Member

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    69 gr bullets work fine in 1/9 twist barrels but no higher. I have made good shots 300-600 yards with 69gr bullets out of a 20" barrel.
     
  16. ny32182

    ny32182 Senior Member

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    My experience is that up to 69gr works well in 1:9 twist; I also fired some 77gr through the 1:9 just to confirm what you read on the internet; sure enough it opened up to about a 5" 20rd group.

    I've shot 77gr in 1:7 with good results.

    As far as 55gr, I find that it shoots fine in 1:7, but overall I've had slightly better accuracy with it in 1:9.

    So my advice is, if you KNOW you will never shoot anything heavier than 69gr, get a 1:9. This actually does cover the vast majority of all commercial and surplus ammo, which is why so many commercial ARs run this twist.

    If you want to shoot heavy bullets, get the 1:7, and you can shoot down to 55gr as well with decent results. I don't know if I'd bother trying to go lighter than 55 with a 1:7 though.

    Personally I own both and probably always will.
     
  17. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

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    An important point to remember is that it isn't the weight that makes a difference, it is the bullet length. Typically; but not always, longer bullets are heavier.

    For example, you may get 62gr .223 to work out of a longer 1/12 twist barrel; but you aren't going to get 62gr M855 to shoot accurately out of the same barrel.

    On a related note, the Barnes TSX 70gr - a commercial hunting load in .223 is even longer than the 77gr Sierra Match King and requires at least a 1:8 twist barrel to stabilize it and is probably better in a 1:7 barrel.

    Also courtesy of kraigwy at TFL, you can find this military chart showing shot dispersion of M193 and M855 ammo through both M16A1 (1:12 twist) and M16A2 (1:7 twist) barrels.

    Short summary: At 274.2m, there was no appreciable difference in group size between M193 55gr fired through a 1:12 twist barrel and M193 55gr fired through a 1:7 twist barrel.

    That reflects my own experiences as well, and since the lightest load I've ever used (45gr WWB JHP) also works fine out of a 1:7 twist, I don't see any point in slower twists that limit my choices at the heavier end. Maybe if I wanted to fire 36gr varmint rounds or could shoot so accurately that hundredths of an inch was a difference I could notice, I would feel differently.
     
  18. minutemen1776

    minutemen1776 Member

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    I have an AR15 with a 1/7 twist and another with a 1/9 twist, and I can tell no difference. Actually, when I first got the 1/7 barrel, I read some THR thread like this and went out and bought some 62-grain loads. It turned out that the 1/7 barrel actually shoots the 55-grainers a little better. The cartridges were of comparable quality, too. Go figure, but don't worry about the twist rate too much.
     
  19. 61chalk

    61chalk Member

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    Thanks for all the info guys! Now for the next test...I'm thinking of seeing
    how many rounds I can put through mine without cleaning an no lube...didn't
    use lube at all until recently, gave it a try an a few rounds later it seemed to
    all burn off anyway. My son has decided to lube his good with synthetic oil.
    We also found out since his upper is used, it shoots wolf steel case no problem
    while my newer upper can't.
     
  20. Zerodefect

    Zerodefect Senior Member

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    Please don't do that. All your doing is finding out when the Ar will fail due to lack of lube.

    I keep the rails on the carrier very wet, the cam pin very wet, firing pin light CLP, Gas rings and bolt hole get rubed down with an oily finger (don't start). I use a 50/50 mix of STP ans ATF. It deosn't move around too much and wipes clean with a little CLP thanks to ATF's cleaning properties. Mobile 1 15w40 works well for me as well.

    Lubed right an Ar will shoot all your SHTF ammo in your truck or pack. Relube afterwards.
    so there is no need to torture test (damage) your AR. You'll run out of ammo before lube usually. In class we spray a little Clp on the Carier between rounds. Takes about 30 seconds.

    I'm sure someone can chime in about when a dry AR will start to jam without you having to abuse it for no reason.
     
  21. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

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    Depends on the environment, rate of fire, ammunition, etc.; but typically they'll start to have stoppages somewhere in the 450-750 round range with no lube and no cleaning.
     
  22. jaholder1971

    jaholder1971 Senior Member

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    Hornady, Federal, Remington, Black Hills, BVAC, Wolf, Prvi, Igman and others all make affordable .223 and 5.56NATO pressure loads in 75 and/or 77 grain bullets.
     
  23. mshootnit

    mshootnit Senior Member

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    1/9 is a better twist for almost all commercial ammo.
    holy crap I just re-replied to a really old thread
     
  24. dogsoldier0513

    dogsoldier0513 Member

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    My 1/7" Colt would shoot Hornady 62gr HPs into 1/4" groups at 100 yards all day long.
     
  25. Sky

    Sky Senior Member

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    I never threw a tennis racket, golf club, or abused anything I can think of. My daddy would have taken it away from me and I would not have gotten it back when I was a kid.

    If I spend hard earned money for something I try to take care of it and with luck it will take care of me. Cars, Airplanes, Boats, guns and women when taken care of all seem to return the favor. If they were a good choice to begin with. errr sometimes errr maybe...well sorry I brought it up!
     

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