Barrel Twist

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    • #102171
      D Close
      Moderator

        No firearms forum would be complete without the obligatory argument for barrel twist preference. I am curious what everyone is running and why and how they tie that into their ammo procurement requirements. I will start it out by saying that I shoot mostly 55gr .223 through a 1/9 5.56mm barrel. I own some M193 and I also own some M855. I’ve stayed away from the heavier bullets. I considered 1/8 but decided against it due to ammo cost. Anything else we should consider?

      • #102172
        Baldrick
        Participant

          As I understand it, and have experienced to some degree. Keep in mind all barrels can shoot all bullets, however you will see some performance difference on certain weights only. For most situations this is marginal, but is differences become more marked at range.

          1/9 excels with 55 gr
          1/8 can shoot everything well from 55 to 77 gr (my barrel of choice)
          1/7 excels with the 69, 75, and 77 gr stuff. But you can still shoot 55 gr through it. Just doesn’t like it as much as the 1/9 does.

          1/8 barrels are widely available and besides the fact that people obsess over mil spec, I don’t know why you would not get a 1/8. When SHTF not all ammo out there will be the current military stuff. YMMV. No doubt s spirited but civil discussion to follow!

        • #102173
          DuaneH
          Participant

            I don’t know it worth arguing about as they will all work. (Amateurs argue gear, experts argue tactics) The only thing I would be aware of is don’t try and shoot 45 grain varmint bullets out of 1/7 twist barrels as it MAY strip the jacket.

            As I understand it(famous last words) the 1/7 was chosen for the military because it is needed to stabilize the longer 62 gr tracer bullets. As I understand it, 1/8 (actually 1/7.7) is optimal for the 62 grain m855.

            My first two ARs had 1/9 twist barrels and were acceptable accurate with 55-62 gr bullets.

            All my AR’s since then are 1/7 (more on that later) there may be 0.5 MOA less accuracy using 55 gr bullets. Hard to tell as M193 are typically more accurate than USGI M855 due to the penetrator core in the M855. I have found USGI m855 to be significantly less accurate than PMC Xtac 62 gr LAP or IMI M855. Quality control went downhill.

            Either way, The 1/7 shoots 55-62 grain good enough to shoot less than 4 MOA at 500-600 meters. I have found accuracy to be more bullet related than barrel related.

            I personally have 1/7 barrels on all my ARs (except my training rifle)

            This is because I live near Palmetto State Armory and the only Cold Hammer Forged Barrels they sell are 1/7 twist.

          • #102174
            JohnyMac
            Participant

              I am using 1:7 twist not because I wanted it but because that is what came with the rifle.

              Just for kicks and giggles and as a comparison to the modern long gun, my black powder rifle has a 1:66 twist.

              I just picked up 4, .223 barrels CHEAP with a 1:12 twist. I haven’t decided what to do with them as yet but again they were CHEAP! Mmmmmm, maybe marry them up with a Mauser or Nagat action? Or maybe a Black Powder .22 :negative: maybe not. However the options are endless.

              DuaneH, I loved your saying, “Amateurs argue gear, experts argue tactics.” :good:

            • #102175
              Corvette
              Participant

                Dave,

                you are right its the obligatory discussion ok, here is my 2 cents on it.

                I prefer 1 in 9 but I run 1 in 7.
                A mystery?

                let me explain
                When the 1in7 rifling was chosen back in the day for the M16A2 style HBars the Army almost chose 1 in 8 or 1 in 9 as the spec.

                Even 1 in 9 is actually quite fast and stabilizes the 62 gr (its actually the length that matters not the grain of the bullets but lets keep it simple) M855 just fine. Just as well as 1 in 7 does.

                1 in 7 rifling is right at the edge what the 62 gr M855 round tolerates ( at least in theory) and is a proper twist for heavier rounds.
                Rumor has it that thinking was to make it possible for those rifle to act as DMR rifles in a pinch with a heavier type match round.
                (M855 meets spec at 4 MOA out of 1 in 7 barrels) :wacko:

                Conversely while contrary to internet lore 1 in 9 does just as well as 1 in 7 w/ M855 62gr.
                The other way around is not as good a match.
                1 in 7 is a bit too fast for 55gr which is the most popular and cheapest 5.56mm ammo.

                HOWEVER in practice it really doesnt matter as much 55gr shoots fin in the real world in a 1 in 7 barrel as does M855 62 gr in a 1 in 9.

                So why are my barrels 1 in 7 if I decided 1 in 9 to be more versatile for me (as I dont shoot match ammo excet in my DMR setup).?

                Simple, the market is chasing “milspec” whether useful or not.
                1 in 7 is “milspec” twist so thats what people want.
                As a result the high end CHF barrels I crave are all 1 in 7.. :unsure:

                PS:
                -M855 LAP ammo is inherently more difficult to manufacture as a accurate round due to the penetrator.. ..
                PS#2: the AR’s with the best reputations for out-of-the-box accuracy are both non-milspec.. 1 in 9′ RRA and Ruger AR’s.. I wonder if there is a connection? ;) )

              • #102176
                Joe (G.W.N.S.)
                Moderator

                  I always wanted to go the other direction, back to the prototype 1 in 14 twist.

                  Depending on the source, the 50ish grain bullets barely stabilized did really effective damage, at the price of somewhat reduced accuracy, and poor arctic performance.

                  Supposedly fine for 200 meter and shorter ranges.

                  It would be a fun experiment.

                  For the most part anything readily available will do a fine job!

                • #102177
                  DuaneH
                  Participant

                    IIRC that was the model they demonstrated to General Lemay where they shot watermelons and they exploded. They then went to 1/12 twist for the above mentioned reasons. http://www.ar15.com/ammo/project/Fackler_Articles/effects_of_small_arms.pdf

                    Good information to know, but most of the work is done by the software.

                  • #102178
                    DuaneH
                    Participant

                      DuaneH, I loved your saying, “Amateurs argue gear, experts argue tactics.” :good:

                      Masters don’t argue at all :-)

                    • #102179
                      Corvette
                      Participant

                        Good stuff Duane! Thanks for posting it! :bye:

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