Can someone explain the need for gain twist rifling?

Discussion in 'Main Message Board' started by jonbearman, Feb 28, 2020.

  1. jonbearman

    jonbearman I live in new york state,how unfortunate ! Gold $$ Contributor

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    I am curious why some shooters swear by it while others are waiting to try it out. What advantage and are there any cons. Just trying to learn.
     
  2. ShootDots

    ShootDots

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    I have ordered one from Bartlein. It is a 9.75 down to 9.30 with conventional 4 groove rifling. I am going to try it because it may (I won't know til I try it) reduce, to some extent, torque. I have started shooting the Berger 30 cal. 230 Hybrids out of a .300WSM. THe bearing surface of the bullet is long and imparts a substantial amount of torque. If I can reduce it, I may be able to shoot better at 1000 yards. We shall see. There are other uses too. Very fast twist barrels like 1-7 have a tendency to blow bullets up in flight. Going from say 7.75 down to a straight 7 may alleviate that problem.
     
  3. Rocketvapor

    Rocketvapor

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    Fast twist in some 223 calibers like 224V, 22N, 22-250, 22-6.5CM can damage a bullet.
    Starting a bullet into a 1:6.5 twist for example.
    7 or 7.5 might be too slow for a heavy, long bullet, 6.5 might be too much to start it.

    The thought is start at 7.5 gain twist up to 6.5.
     
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  4. ShootDots

    ShootDots

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    There is some formula that Bartlein uses to determine the "best / correct" gain twist for a given caliber. I believe that 6mm are different than 7mms and 30s different from 7mms etc.. Placing a call to them will get someone on the right track..
     
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  5. 6ShotsOr5?

    6ShotsOr5? Gold $$ Contributor

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    Lots of interesting ideas here. A gentleman from Patriot Valley Arms — not the owner — told me that his understanding was that fast twist increased throat erosion and that if you started with a slower twist and finished at the desired twist for bullet stability you could increase barrel life. If that or the torque issue @ShootDots mentioned are true I don’t know why you wouldn’t want to start with almost no twist. I have no personal experience but would like to try a gain twist sometime.
     
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  6. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    Bartlein has been doing them for many years. Kinda like a 5r i guess- not for me
     
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  7. kvd

    kvd Silver $$ Contributor

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    There is probably some pressure extreme that would simply squirt the bullet out of the barrel without ever engaging the rifling - literally ripping it apart. Gain twist barrels may allow one to shoot a higher pressure by easing the transition from not spinning while sitting in the chamber to a relative fast spin in a couple feet of barrel length. I can see where a gain twist would help with the initial torque as well.

    The comment above makes sense. Starting out with a mild twist rate and accelerating the rate of spin down the barrel as the intense initial impulse pressure is turning into more of a very strong push seems like a good idea. Starting out at 30:1 or 40:1 and increasing steadily in the middle of the barrel, ending up with the fast spin rate required to stabilize long, heavy bullets sounds good theoretically. Might be difficult to produce such a barrel though and it may need to be 35 or 40 inches long to accomplish the desired transition.
     
  8. spclark

    spclark Gold $$ Contributor

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    Don’t count on it.

    Moderate change in twist rate doesn’t affect the shape of the lands & grooves as much as a more drastic change in barrel lengths we view as appropriate.

    The effect of a change in twist rate on a jacketed bullet begins with a slower acceleration of rotation as the bullet fully engages the rifling, easing the stresses imparted on jacket and core.

    Practical limits on barrel length leave us with no choice but for moderate twist rate changes, as more drastic rates of change in barrels of reasonable length would distort rifling to a point that bullets might literally be “ripped apart” from the varying twist imparted by the changing shape of the rifling. Longer bearing-surface bullets would be affected most.

    A little of a good thing more often has fewer, less drastic side effects than a lot.
     
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  9. clowdis

    clowdis

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    Gain twist was popular back in the late 1800's when Harry Pope and others started using it to accelerate the spin on lead bullets for match shooting. The gain twist started the bullet slower so that the faster twist wouldn't distort the bullet. I don't think it has ever been proven to be more accurate with any kind of bullet or in any kind of shooting.
     
  10. golong

    golong

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  11. rkittine

    rkittine Gold $$ Contributor

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    Interested reading on their web site. Thanks for posting the link.
     
  12. Texas10

    Texas10 Gold $$ Contributor

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    Bullets go to sleep in the barrel without gain twist?!

    They start easier with a gain twist?

    I frequently pick up spent 30 cal bullets at the range, some in nearly perfect condition with the land indentations unmolested. I would like to see what a gain twist barrel does to the copper jacket where the lands are swaging a new angle into the jacket as it moves down the bore. That would clear up a lot of questions.
     
  13. Rocketvapor

    Rocketvapor

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    The difference over the length of a 24" barrel with a 7.5 to 6.5 linear gain would be about 0.021" for a 1/2 inch bullet bearing surface.
    Unless you could compare the engraved bullet to the original land, how would you know?
    The final engraved angle would be the result of the final twist.
    Did I calculate that right?
     
  14. 6ShotsOr5?

    6ShotsOr5? Gold $$ Contributor

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    That makes sense @spclark, thanks for explaining that.
     
  15. sw282

    sw282

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    ltalian 6.5 Carcano had a gain twist barrel as does some of the S&W X Frame 500s.
    Some of the Big Naval guns (Rifles) had it too
     
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  16. Bill K

    Bill K Silver $$ Contributor

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    Wasn't it used with the theory that pressure would not build up as fast, when you fired a round ?
     
  17. 6fatrat

    6fatrat SLING SHOOTER Silver $$ Contributor

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    Beats me????
     
  18. Texas10

    Texas10 Gold $$ Contributor

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    The idea of Gain Twist came about in the era of lead bullets propelled by black powder. WWII Naval guns used black powder too along with gain twist (see above link provided by @golong). The powder elevators on the Mighty Mo were featured in a Steven Seagal and Tommy Lee Jones 1992 movie Under Siege. Also featured a memorable scene with Playboy Centerfold Erika Eleniak.:cool:

    Given the lesser mass and harder jacket material of today's match bullets as compared to old school large caliber lead bullets, I question the benefits of gain twist being applicable to today.

    As always, I'm open to being proved wrong...LOL
     
  19. kvd

    kvd Silver $$ Contributor

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    Yes - you are correct. I didn't think about how the lands and groves engraved on the bullet from the original rate of twist would be distorted as they followed the new ever increasing twist rate. Thank you for pointing that out.
     
  20. D Coots

    D Coots Silver $$ Contributor

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    It was said above gain twist reduces torque.

    Wouldn't spinning a bullet faster create more torque?
     

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