twist rate in ar 15

papabear68papabear68 Posts: 13 New Member
what twist rate would have the best accuracy?

Replies

  • ZeeZee Senior Member Posts: 20,564 Senior Member
    Typically matched towards intended bullet weight. 

    Lighter bullets can be shot in a slower twist but heavier bullets need a faster twist. 

    I tend towards faster twists regardless as I can shoot borh heavy and light bullets. 

    Personally, I prefer 1-7” twist rate on a barrel.  The slowest I will buy is a 1-9” twist. 

    That’s my preference and it has worked with bullets from 50gr up to 80gr. 
    "To Hell with efficiency, it's performance we want!" - Elmer Keith
  • papabear68papabear68 Posts: 13 New Member
    I am gonna probably shoot 55-75 grain bullet.  the ar15 that I am looking to assemble has a 1-7 twist
  • ZeeZee Senior Member Posts: 20,564 Senior Member
    The twist has to do with the stabilization of a bullet of a certain length (weight). Heavier bullets tend to be longer and therefore need a faster twist to stabilize them. 

    Accuracy, assuming the bullet is stabilized with a proper twist, has more to do with the barrel liking a certain bullet/load combination. 

    Its a deep rabbit hole. 
    "To Hell with efficiency, it's performance we want!" - Elmer Keith
  • papabear68papabear68 Posts: 13 New Member
    thanks for your help
  • jbohiojbohio Senior Member Posts: 5,499 Senior Member
    Well, Zee pretty much said it all.  
    I have a 1:9 that shoots very well, but I stick to 55-62 grain bullets.
    Most of the others are 1:7.


  • BigslugBigslug Senior Member Posts: 6,939 Senior Member
    The ORIGINAL reason for the 1-7" on the twist in the M16A2 was military tracer ammo.  These slugs needed to be longer to hold the burn elements in their tail.  The 1-7" and 1-8" twists have become the thing for the 70-80 grain bullets used in Highpower matches (peaking out at 600 to 1000 yards, depending on the exact discipline).  There are also a few heavier military and LE loads out there that will need the faster spin.

    The opposite end of the military scale was 1-14" on the earliest M16's.  These were deliberately about barely stabilizing a 50-55 grain bullet to help it tumble on impact.  It had trouble in thick, cold, sea-level arctic air, so the most-produced variant (M16A1) ended up with 1-12".

    There's some argument that the 1-9" twist may do better for the light to middle weight bullets under 70 grains, but I don't spend a lot of time sweating it.  The 1-10" twist you see in a lot of .30 calibers is a holdover from the pre-spitzer days of 200+ grain bullets, but I've seen plenty of bughole groups shot with 150 and lighter from tubes so equipped.

    I tend toward the 1-7" twist that will stabilize any random ammo I encounter well enough for government work - even though they can be made to do it, AR's are simply not the guns I care about getting supreme accuracy from.  If you're looking for a true precision match shooter, the first thing you'll want to do is trade away durability for uniformity of bore by giving up a chrome-lined barrel in favor of a high-end stainless number.  After that, select the twist most appropriate to the bullets you intend to shoot.  THEN you need to consider whether you want the safety of a longer 5.56 throat designed specifically for high-pressure, mil-spec ammo, or the higher accuracy potential of a tighter .223 chamber  that will require loading to lower pressures to avoid blowing primers, OR go even deeper down the rabbit hole with the "in between" Wylde spec.

    In short, where are you trying to end up?
    WWJMBD?

    "Nothing is safe from stupid." - Zee
  • bullsi1911bullsi1911 Moderator Posts: 9,661 Senior Member
    Zee said:


    Its a deep rabbit hole. 
    Yes it is.
    To make something simple is a thousand times more difficult than to make something complex.
    -Mikhail Kalashnikov
  • AccipiterAccipiter New Member Posts: 59 Member
    I stick to 1/7 or 1/8.  Zee stayed the whys.
  • SpkSpk Senior Member Posts: 1,948 Senior Member
    edited March 3 #10
    Give us a guesstimate on range and varmint type and you'll have lots of recommendations.
    Beware of false knowledge -- it is often more dangerous than ignorance.
  • VarmintmistVarmintmist Senior Member Posts: 6,460 Senior Member
    Just for reference I shoot a 77 across the course 200-300-600 and it seems to work pretty well out of a 1:7. I do load the 600 yard stuff a bit longer as it doesnt have to feed through a magazine.
    It's boring, and your lack of creativity knows no bounds.
  • snake284snake284 Senior Member Posts: 21,802 Senior Member
    edited March 4 #12
    I've shot 65 and 68 grains out of my 1:9 twist barrel but that rifle, a Stevens Model 200 isn't a real tight grouper except with one bullet so far, a Hornady 68 grain BTHP Match. It shoots those under a half minute. All else both heavier and lighter are 1.5 to 2 MOA. That rifle's weird.
    Daddy, what's an enabler?
    Son that's somebody with nothing to do with his time but keep me in trouble with mom.
  • snake284snake284 Senior Member Posts: 21,802 Senior Member
    I am gonna probably shoot 55-75 grain bullet.  the ar15 that I am looking to assemble has a 1-7 twist
    I think you're covered with a 1:7. That's about the max for a .223. My new AR I'm having built is going to have a 1:8 but 70 grains are about as heavy as I'll shoot.
    Daddy, what's an enabler?
    Son that's somebody with nothing to do with his time but keep me in trouble with mom.
  • bisleybisley Senior Member Posts: 10,549 Senior Member
    I like the heavier bullets, 64 grain and up, so I have 1:7 and 1:8. The 1:8, shooting 68 grain Hornady Match bullets, at max 'book' charge is the most accurate rifle I own, a 20" heavy barrel. I can shoot 70 grain Barnes TSX, for hunting, with no noticeable accuracy decline, from a field rest.

    The 1:7 16" medium contour barrel is for plinking and home defense, and mostly is used with 64 grain steel core hand loads, or 64 grain Gold Dots.
  • papabear68papabear68 Posts: 13 New Member
    it would be basically for coyote.   range 100-400 yds. I can barely see past that  haha
  • bisleybisley Senior Member Posts: 10,549 Senior Member
    edited March 5 #16
    My 1:8 20" barrel was intended to be my 'varmint rifle,' with 70 grain Barnes TSX, because I can maintain sub MOA groups at 300 yards, with a makeshift field rest. I'm quite sure that the more serious riflemen could do much better with the same set-up, at longer ranges. I don't practice enough to be that good, so I settle for MOA at 300 yards, as my personal benchmark.
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