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  • twist rates

    Question:

    I have read here before the opinions about the 1:10 versus the 1:12 twist rates. 1:10 being for heavier bullets (175-220 grain) and 1:12 being for lesser grain bullets (155-175 grain). Has anyone ever tried a middle twist, like 1:11? I have even heard of a .308 utalizing a 11.25 twist rate. What would you expect from a barrel with this twist rate for a .308, speeking range/grouping wise with a 175 grain bullet?

    Assuming your using a 26 inch barrel.

    Vern and Jered please feel free to chime in on this one.

  • #2
    Hunter:
    Try this page:

    http://www.eskimo.com/~jbm/calculations/drag/drag.html

    For a 175gr bullet, with all other things except twist rate being equal, this page gives a "stability" at an MV of 2500 FPS (not what you'd be shooting at, but ok for relative comparisons between different twists) of:

    Twist Stability
    10.0 1.658
    11.25 1.310
    12.0 1.151

    In this case, a bigger stability is better.

    Cheers,
    --Hawk
    There are few problems a well-placed 308 cannot cure. --- Hawk

    Gentlemen! You can't fight in here! This is the War Room! --- President Merkin Muffley in Dr. Strangelove

    Rocket Science is much more fun when you actually have rockets! --- USN Recruiting Commercial

    A little revolution now and then is a good thing --- Thomas Jefferson

    Only the dead have seen an end to war --- Plato

    "In Ireland, in Lebanon, in Palestine & Berkeley, Patty Hurst, heard the burst, of Roland's Thompson gun & bought it!!!" --- The Late Warren Zevon, Roland The Headless Thompson Gunner

    In the 1500's, the Roman Catholic Church sold indulgences to forgive sin. In the 21st century, we call these carbon offsets. ---Hawk

    �Fight like a man, so you will not have to die like a dog� --- Calico Jack Rackham's Mistress

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    • #3
      I use a 1:10 and it shoots both the 168's and 175's equally well. I haven't tried any other weights out of it yet, and probably won't.
      www.precision-applications.com

      It's knowing that when I get up in the morning and my feet hit the floor, the Devil says, "Shit! He's awake!"

      Shortly before World War I, the German Kaiser was the guest of the Swiss government to observe military maneuvers. The Kaiser asked a Swiss militiaman: "You are 500,000 and you shoot well, but if we attack with 1,000,000 men what will you do?" The soldier replied: "We will shoot twice and go home."

      "There are so many Russians, and our country so small, where will we find room to bury them all?" - anonymous Finnish soldier

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      • #4
        My 1:10 shoots both great as well. I like it for the 175's at range. The 168's did a ragged whole at 100. I can't complain about either.
        "Do the right thing even if it means dying like a dog when no one's there to see you do it." Vice Admiral James Stockdale, NAVY PILOT

        "Honor, Integrity, Commitment to core values. When they become abstract concepts or "ideals", all is lost." Me.

        "Character is doing the right thing, even when no one is looking." J.C. Watts

        "I have never seen a projectile turn in flight and come back at the ship that fired it, I cannot however make that same statement regarding missiles." Me.

        Deus lo vult! = "God wills it!"

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        • #5
          Here's a pretty good article at the Lilja barrels website on bullet stability as related to twist rate and atmospheric conditions:

          http://www.riflebarrels.com/articles/bulle...fling_twist.htm

          Seems a stability factor of 1.3 is the minimum recommended. Given that, it looks to me like the 11.25 twist is just barely good enough for a 175gr bullet.

          Savages have a twist of 1:10. Guess what Remmys have? 1:12. Yet another reason to buy a Savage!

          Cheers,
          --Hawk
          There are few problems a well-placed 308 cannot cure. --- Hawk

          Gentlemen! You can't fight in here! This is the War Room! --- President Merkin Muffley in Dr. Strangelove

          Rocket Science is much more fun when you actually have rockets! --- USN Recruiting Commercial

          A little revolution now and then is a good thing --- Thomas Jefferson

          Only the dead have seen an end to war --- Plato

          "In Ireland, in Lebanon, in Palestine & Berkeley, Patty Hurst, heard the burst, of Roland's Thompson gun & bought it!!!" --- The Late Warren Zevon, Roland The Headless Thompson Gunner

          In the 1500's, the Roman Catholic Church sold indulgences to forgive sin. In the 21st century, we call these carbon offsets. ---Hawk

          �Fight like a man, so you will not have to die like a dog� --- Calico Jack Rackham's Mistress

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          • #6
            A quality (this means this is the REAL twist) 1-12" works great with 175 SMKs. Berger bullets are longer than SMKs, and theoretically need a faster twist rate, yet the manufacturer recommends a 1-13" twist.
            http://www.bergerbullets.com/catalog.htm
            In any case, with a slightly faster twist than needed AND high quality bullets there's only a minute degradation in accuracy, so a faster twist does not matter much in real life.

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            • #7
              The new USMC M40A3 barrel is a Schneider and cut to 24" from the recoil lug to the muzzle. This is a change from how barrels are normally measured and really should be called a 25" barrel. It has a 1/12 inch twist and shoots the M118LR 175 match ammo with no problem.

              I own an M40A1 built to Marine Corps specs except with a 26" barrel and it can handle the 175 gr very well. It has a Hart barrel with a 1/12 inch twist.

              Tom
              T.Bruner

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              • #8
                Depending on barrel length the 1-12 is a grey area for the 175's. Not that they won't shoot but we are looking for optimal not a hit. The 1-12's on longer tubes gives you maximum velocity. Sometimes you may need a slightly warmer load than some factory stuff to do well at extended ranges. When it comes to off the shelf ammo I'd prefer a 1-11 or 1-11.27. It will shoot the factory stuff with better over all results. As far as the 1-10. I rarely use them unless someone wants to shoot 190's + or they want to shoot some subsonic stuff.

                Hope this helps

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                • #9
                  My rifle has a 26" Hart Barrell with 1 in 12" twist. It handles 175 grain SMK with no problem. Maybe not optimum stability, but but repeatable accuracy, which is what counts.

                  James
                  "Ever since I was a kid I've had snakes as pets. They're clean and quiet. You give them rodents and they give you pure, unconditional indifference." Carl Hiaasen

                  "The Constitution is NOT and instrument for the government to restrain the people, it IS an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry

                  "War was always here. Before man was, war waited for him. The ultimate trade awaiting its ultimate practitioner." ? Cormac McCarthy

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                  • #10
                    If you buy a used rifle and don't know the twist rate is there a way to find out?

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                    • #11
                      Put a patch on your cleaning rod and put it in the barrel until it engages in the rifling, marking it for a reference. Push the rod into the barrel until it makes one complete rotation and mark again. Measure between the marks. If the rod goes 12", it's 1 in 12, etc.
                      "Do the right thing even if it means dying like a dog when no one's there to see you do it." Vice Admiral James Stockdale, NAVY PILOT

                      "Honor, Integrity, Commitment to core values. When they become abstract concepts or "ideals", all is lost." Me.

                      "Character is doing the right thing, even when no one is looking." J.C. Watts

                      "I have never seen a projectile turn in flight and come back at the ship that fired it, I cannot however make that same statement regarding missiles." Me.

                      Deus lo vult! = "God wills it!"

                      Comment


                      • #12
                        I've been shooting matches for over 35 years. For the 308 and a 175, which has only been out about 15 years, I have not really seen a difference. With a 26" barrel I've shot .5 moa at 1000 yds with a 1 in 12 twist. However I seem to be able to do it with more frequency whenI use the 1 in 10. I shoot 1000's of bullets each year here at the farm.

                        Day in day out, I feel the 1 in 10 is the best. When your trying to get extreme spreads down, I find I do it faster with a 1 in 10 twist. With all the different bullets, like M 118 LR, Fed. Match, BH's and handloads, for me they all seem to shoot better again in a 1 in 10.

                        I believe however if you use a 24" barrel you should use a 1 in 11 twist barrel. I found the Kreiger 1 in 11 twist, 24" four groove barrel to be able to hang moa for moa at 1000 yds.

                        Over the last 30 + years I've seen folks trying to reinvent the wheel over and over. About every 10 years or so this keeps coming up with the twist rates. Fact is with a 175 grain bullet, playing with about 40 fps spread any of those twists will work. I again do feel the 1 in 10 will produce between extreme spreads.

                        flea
                        "with the patience of an oyster....I watch and wait"

                        Training the US, one shooter at a time.






                        http://www.centralvirginiatactical.com

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                        • #13
                          I use a Patriot rifle with a 22" 1-12 Hart barrel and 175's.
                          I shoot out to 1,000 yards up at Flea's and it seems to hold fine. I got 5 consecutive hits on Flea's 10"x10" plate at just over 1,000 yards the other day.
                          Patriot is building me a new rifle with a 24" Mike Rock 1-11.27 barrel and I plan on shooting 175's from this as well. I'm looking forward to comparing the performance at long distance.
                          "Kill evil. It's how quality of life is achieved. Carry on."---Ted Nugent

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                          • #14
                            The exceptions to the rule can be interesting. My match rifle has a 1:13 twist 30" Krieger, intended for best results with the 155 grain bullet. Have found that it also shoots 168's and 175's quite well. Some of my BR buddies shoot lightweight flat base bullets from even slower twist barrels that are remarkably accurate.

                            This year the top gun at the Palma tryouts used a 1:10 twist barrel and 155 grain Berger VLD's. Too fast of a twist for the 155's according to conventional wisdom, but he did finish first. Hard to argue with success!

                            The 24" 1:12 twist Krieger on my tactical rifle handles 110 V-Max, 155 A-Max, 168's and 175's equally well. Maybe a slight preference for the 168's. Also shoots 165 SPBT Sierras well.

                            FWIW, Guy

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                            • #15
                              Hi,

                              I know this is an old topic and much discussed issue, but nevertheless a few comments.

                              Very good and informative hands on experiences from all the Gents above.

                              And yes, we all know the so called main rules of determing a twist rate. But as Flea pretty much summarized it all, the best bet for heavy bullets is 1:10 rate and for lighter bullets 1:12 rate; and 1:11 rate falls in btw these two as a compromise.

                              However, there are so many interesting exceptions to the rule like M700 referred - well pointed out M700; really hard to argue with success - I agree.

                              Furthermore, Thomas W Bruner also pointed well out that 1:12 rate works fine with heavy bullets in M40 series rifles.

                              I'm really interested in finding reasons for these exceptions, since I have similar practical experiences from the field during past yrs. There has to be a logical and rational reason for the exceptions. What it is, I don't know, but I try to figure it out.

                              A recent field example: Shooting 155 gr Scenars 1:10 twist rate worked perfectly well from short barreled 20" semiauto and bolt rifles in .308 caliber at 1000 meters. Also 1:11 twist rate worked similar ways, but not 1:12 rate. Why so? 1:12 twist rate semis and bolt guns were GTG up to 900 meters (20" barrel) and as said already 1:10 & 1:11 semis and bolt guns were GTG up to 1000 meters (20 "barrel).

                              I would say that light bullets (let's say 145 - 155 gr) overstabilze when shooting from a 20" barrel with 1:10 twist rate and at the extreme max. distance let's say 1000 meters (the distance where one can still engage and hit targets and the bullet is still supersonic and stabilized > round bullet holes in the target), the bullets are still stabilized due the higher start spinning rate and thus enable bullets to score, while still being supersonic - this was of course simplified example.

                              Wheathers light bullets (145 - 155 gr) are pretty much stabilized already all the way when shooting from a 20" barrel with 1:12 twist rate and at the extreme max. distance 1000 meters aren't any more stabilized due to the slower start spinning rate and thus aren't able to produce score - they are still supersonic though.

                              Twist rate 1:11 is a compromise btw these two above twist rates and seems to work alright at least so far.

                              With longer barrels, over 20", light bullets (145 - 155 gr) seem to stabilize well regardless of twist rate. Therefore, taken the above example, all twist rates 1:10, 1:11 and 1:12 are GTG at 1000 meters; bullets are stabilized (round bullet holes) and naturally supersonic.

                              Why is that? Is it due to extra velocity gained from longer barrel? Quite likely maybe, hard to say.

                              Nevertheless, an interesting issue, not trying to reinvent the wheel, just merely find the logic and rationality behind these exceptions.

                              Just my two cents.

                              Shoot well !

                              Cheers,

                              Mace

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