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RIFLE TWIST

Discussion in 'General Firearm Discussion' started by doubletap007, Dec 19, 2011.

  1. doubletap007

    doubletap007 Beaverton Active Member

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    I have a question on rifle twist I would like to hear some expert advise on.
    So I have always understood that the tighter the twist rate was the more accurate the barrel is.
    I just met a guy last week with a lot of experience with ar type rifles and he said it is not true that a 1:10 twist would be superior to a 1:11.25 twist although the match barrel i was looking for was a tighter twist than my stock ar10 1:11.25 twist.
    i was looking at lmt barrels and the 20"chrome lined barrel was only $485 with a 1:10 twist while the $700 stainless barrel was 1:11.25 twist.
    this guys thory is that the higher twist ratio(1:11.25) makes the bullet come out flipping and causing a more vicious wound than a tighter twist would without sacrificing accuracy while a tight 1:9 or 1:10 twist will just penetrate with much less damage and
    this just making a more desireable round for nato due to the geneva convention act making gunshots more survivable but not more effecient persay.
    what say you about the accuracy at long ranges between the two vs.damage inflicted?
    since i dont plan on going to war anytime soon i just want a more accurate long range barrel and lets face it a 7.62x51mm is going to do damage no matter how it hits you.
     
  2. speedtriple

    speedtriple Vancouver, Washington, United States Member

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    You are going to get replies from people who know and understand this much better than I.....
    The proper twist rate varies with the style bullet you want to shoot. Barrels with slow twist rates, like a 1:12, are designed for smaller bullets. They don't take as much speed to stabilize during flight. Faster rates are required for larger bullets so they will stay stable throughout the flight. If you put a small, light bullet through a fast rate barrel, they may spin so fast they come apart. A big heavy bullet through a slow rate barrel may start tumbling before it gets to the target.

    Look at the twist rates on bolt action/varmint .223. They are slow because most varmint bullets are small and light. On a AR style .223, the twist rates are faster, so stabilize the larger bullets usually used for, well larger targets. Hope this helps until and expert chimes in.

    Gregg
     
  3. Dutchy556

    Dutchy556 Bend, OR Member

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    Speedtriple has the gist of it. Twist rate corresponds with accuracy in the sense that certain twist rates are better suited to stabilizing specific bullet weights. The heavier (longer) the bullet is, the the faster the twist rate required for optimal stability.

    What are bullets are you planning on shooting?

    I've had excellent results with my OBR, which is 1:11.25, with everything from 155s to 175s. I had a Rem 700 AAC with a 1:10 barrel that really seemed to prefer the 175s (heaviest I used in it) but also did ok with 168s as well. The 1:10 is generally better suited to the heavier .30 bullets you'll be pushing out of a 7.62x51/.308. For good all around performance with a wide variety of bullets I'd go 1:11.25.

    As for that stuff about the bullet "flipping around" and whatnot... yeah, no. The terminal effects of the round are determined by bullet weight, construction and velocity.
     
  4. Greenbug

    Greenbug Bend Well-Known Member

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    There seem to be lots of folkes out there with guns that shoot bullets like they came out of a sling shot rather than a rifled barrel.

    If you are shooting up to 168 grain bullets go with the 1:11.25 twist.

    If you are going to shoot heavier than 168 grain bullets go with the faster 1:10 twist.

    Personally, just go with the 1:10 twist barrel and shoot any bullet weight your gun likes.
     
  5. Nwcid

    Nwcid Yakima and N of Spokane Well-Known Member

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    The very simple answer is this. A bullet has to spin to be stable. To get the bullet spinning it has to have rifling. Rifling twist is based on the length of the bullet ie the amount of contact surface between the barrel and bullet. Many people use weight for twist rate but this is because heavier bullets are longer.

    BTW a 1 twist in 11.25" (1:11.25) is SLOWER then a 1 twist in 10" (1:10). Again the proper twist will depend on the length of bullet you want to shoot.
     
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  6. Mark W.

    Mark W. Silverton, OR Bronze Supporter Bronze Supporter

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    My .243 has a 1-9.25" twist my 30-06 has a 1-10 twist my .50 cal muzzle loader has a 1-72" twist (target barrel designed for round balls) Twist rates have a lot to do with the lenght of a bullet for a given caliber. A long bullet tends to require a different rate then a short bullet.
     
  7. doubletap007

    doubletap007 Beaverton Active Member

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    good info guys,these all make a lot of sense,good knowledge on this forum!
    i did notice when looking at armalite my barrel the stock 20"double lapped 1:11.25 was recomended to shoot 150~175gr while the match grade triple lapped barrel 1:10 twist was recomended for 168gr~185 and says will stabilize 200gr ammo.but both barrels recommend 168gr as a well rounded bullet.this make sense now.
     
  8. civilian75

    civilian75 Hillsboro, OR Well-Known Member

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    Those number sound about right. One thing, though. 7.62x51/308Win will shoot bullet very efficiently up to about 180gr. from that point on, the bullet weight to performance starts to diminish rather rapidly. That's were .30-06 shines v. 308Win. This appears pretty accurate at least with the powders I know off. Maybe newer powders I don't know of can help stretch the performance curve.
     
  9. mjbskwim

    mjbskwim Salmon,Idaho Well-Known Member

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    These guys are all being nice and have better answers than I could give...except don't ever ask your buddy about guns again.
    Never heard of any rifle that was designed to make the bullet flip around to cause more damage
     
  10. hermannr

    hermannr Okanogan Highlands Well-Known Member

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    The real deal is the sectional density, the high weight (longer bullet) wants a faster rate of twist, the little short stubby bullets like a longer twist. Has nothing to do with caliber, has everything to do with the contact area of the bullet to the lands in the barrel.

    If you are into precision shooting, I would go to a custom barrel maker and ask what he would recommend for a particular bullet for a particular caliber and then do all of my precision shooting with that bullet. For example, my 700 is set up to do it's best with 142 gr Sierra Match bullets. That does not mean I can't shoot 100gr hollow points when I want to shoot coyotes instead of paper, it is just the 100 gr won't go sub 1/2 minute, where the 142gr will. (.264/6.5mm bullets)
     
  11. deen_ad

    deen_ad Vancouver, WA Well-Known Member

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    I could never do the twist with a rifle, not even when I was younger :stretcher: :laugh:
     
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  12. rrojohnso

    rrojohnso Vancouver, WA Member

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    Here is a link to a great site discussing this: Topic of the Month

    I am reading a large book right now that says using this specific equation can reduce your time in finding the optimal bullet for accuracy.
     
  13. civilian75

    civilian75 Hillsboro, OR Well-Known Member

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    Most variables could be summed up in one term: "rotational moment of inertia" when analyzing rifle twist ratios. Back in engineering school I always wondered if I'd ever be using any of those Dynamic Mechanics knowledge they tried to stuff into my brain. Many years later and countless beer some of it is still left.

    When calculating rotational moment of inertia, the whole bullet geometry and composition needs to be considered. If looking at geometry or shape, whether it is pointy (tangent ogive, secant ogive, cone shaped, etc), round nose, has a boat tail, meplat diameter, etc. When looking at the composition you need to understand its density (lead, steel, brass, copper cores), or if it homogeneous like cast and un-jacketed swagged bullets, or if the bullet has void between the jacket and the lead core, like Russian 7n6 5.45x39 bullets. Two bullets may have same weight and almost identical length, but are otherwise different in the areas mentioned above, one may stabilize and the other may stumble at certain twist ratios.

    And then there are the environmental variables, but that is way beyond my understanding....

    Several years ago I found online a free internal ballistics program with a twist rate tool that goes way beyong the Greenhill formula. But for the life of me I can't seem to find the link to their page.
     
  14. Jerry

    Jerry Vancouver, WA Well-Known Member

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    Here's a few things regarding twist rates that I found interesting:

    Sir (Alfred) George Greenhill, F.R.S. (29 November 1847, London — 10 February 1927, London), was a British mathematician.
    George Greenhill was educated at Christ's Hospital School and from there he went up to St John's College, Cambridge in 1866.[1] In 1876, Greenhill was appointed professor of mathematics at the Royal Military Academy (RMA) at Woolwich, London, UK.[2] He held this chair until his retirement in 1908. His 1892 textbook on applications of elliptic functions is of acknowledged excellence.
    In 1879, Greenhill developed a rule of thumb for calculating the optimal twist rate for lead-core bullets. This shortcut uses the bullet's length, needing no allowances for weight or nose shape.[3] Greenhill applied this theory to account for the steadiness of flight conferred upon an elongated projectile by rifling. The eponymous Greenhill Formula, still used today, is:

    where:
    • C = 150 (use 180 for muzzle velocities higher than 2,800 f/s)
    • D = bullet's diameter in inches
    • L = bullet's length in inches
    • SG = bullet's specific gravity (10.9 for lead-core bullets, which cancels out the second half of the equation)
    The original value of C was 150, which yields a twist rate in inches per turn, when given the diameter D and the length L of the bullet in inches. This works to velocities of about 840 m/s (2800 ft/s); above those velocities, a C of 180 should be used. For instance, with a velocity of 600 m/s (2000 ft/s), a diameter of 0.5 inches (13 mm) and a length of 1.5 inches (38 mm), the Greenhill formula would give a value of 25, which means 1 turn in 25 inches (640 mm).


    As a general rule:
    • The higher the velocity, the slower twist is required.
    • The lower the velocity, the faster twist is required.

    Rifle barrels are designed to incorporate lands and grooves that spin the projectiles they fire so that they will fly true and hit point-on. That is the fundamental definition of a rifle, it uses a rifled barrel. Rifle barrels are grooved so that the bullet makes one complete turn in a given number of inches on its trip down the barrel.

    What follows is a list of the rates of twist for common rifle cartridges. These were taken from various sources. The rates of twist below are expressed as "one complete turn in so many inches" (i.e. 1 in 9", 1 in 10", etc.).
    .17 HMR = 1 in 9"
    .22 Long Rifle = 1 in 16"
    .222 Remington = 1 in 14"
    .223 Remington = 1 in 12"
    .22-250 Remington = 1 in 14"
    .223 WSSM = 1 in 12"
    .243 Winchester = 1 in 10"
    6mm Remington = 1 in 9"
    .243 WSSM = 1 in 10"
    .240 Wby. Mag. = 1 in 10"
    .25-06 Remington = 1 in 10"
    .257 Wby. Mag. = 1 in 10"
    6.5x55 Swedish Mauser = 1 in 7.5"
    .260 Remington = 1 in 9"
    .264 Win. Mag. = 1 in 9"
    .270 Winchester = 1 in 10"
    .270 WSM = 1 in 10"
    .270 Wby. Mag. = 1 in 10"
    7x57 Mauser = 1 in 9"
    7mm-08 Remington = 1 in 9.25"
    .280 Remington = 1 in 9.25"
    7mm Rem. SAUM = 1 in 9.25"
    7mm WSM = 1 in 9.5"
    7mm Rem. Mag. = 1 in 9.25"
    7mm Wby. Mag. = 1 in 10"
    .30 Carbine = 1 in 16"
    .30-30 Winchester = 1 in 12"
    .300 Savage = 1 in 10"
    .308 Winchester = 1 in 12"
    .30-06 Springfield = 1 in 10"
    .300 Rem. SAUM = 1 in 10"
    .300 WSM = 1 in 10"
    .300 Win. Mag. = 1 in 10"
    .300 Wby. Mag. = 1 in 10"
    7.62x39 Soviet = 1 in 7.5"
    .303 British = 1 in 10"
    .32 Win. Spec. = 1 in 16"
    8x57 JS Mauser = 1 in 9.25"
    .338-57 O'Connor = 1 in 10"
    .338 Win. Mag. = 1 in 10"
    .340 Wby. Mag. = 1 in 10"
    .357 Mag. = 1 in 16"
    .35 Remington = 1 in 16"
    .35 Whelen = 1 in 16"
    .350 Rem. Mag. = 1 in 16"
    .375 H&H Mag. = 1 in 12"
    .378 Wby. Mag. = 1 in 12"
    .416 Rem. Mag. = 1 in 14"
    .416 Wby. Mag. = 1 in 14"
    .44 Rem. Mag. = 1 in 20"
    .444 Marlin = 1 in 20"
    .45-70 Govt. (Marlin and Ruger rifles) = 1 in 20"
    .450 Marlin = 1 in 20"
    .458 Win. Mag. = 1 in 14"
    .460 Wby. Mag. = 1 in 16"
     
  15. civilian75

    civilian75 Hillsboro, OR Well-Known Member

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  16. iamme

    iamme Lane County Well-Known Member

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    List has .223 at 1/12?? hahaha.

    FWIW- Savage uses 1/10 on most their factory barrels, I believe on their 5r it's 1:11.25. Basically one twist rate with one type of rifling will/may shoot different than a barrel of same twist but different rifling.
     
  17. coop44

    coop44 Tacoma ,WA Well-Known Member

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    5.56 1/7 twist spins a bullet somewhere around 30,000 rpm, oops I meant 300,000rpm
     
  18. Gunner3456

    Gunner3456 Salem Well-Known Member

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    Rifle twist? Oops, wrong thread.

    addddddcopy.jpg

    addddddcopy.jpg
     
  19. Gunner3456

    Gunner3456 Salem Well-Known Member

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    Almost.

    It's only the length, not the weight which matters. Longer bullets in a given caliber will need a faster twist rate.

    The military went to 1:7 (fast) twist rate in the 5.56 because they were shooting tracers which are very long but very light weight. Then they went to 62gr bullets which are longer than the 55gr they had traditionally used, because the 55gr were too short for the 1:7 twist.

    In 'Nam, they started with 55gr and 1:15 twist, then found that 1:12 twist was better for that round. For those of us who want civilian guns with a range of ammo, 1:9 is nice because it will do real well with 55 and 62, and manage OK for everything else. 1:7 is OK for 62 and up for the target shooters.
     
  20. Spitpatch

    Spitpatch Forest Grove, Oregon Well-Known Member

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    Longer------Faster

    Shorter-----Slower.

    Memorizing technique: Jackrabbit vs. Turtle.