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Gain twist vs conventional twist

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/26/2017 at 06:33
nralifer View Drop Down
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Would like to see what guys on the forum think about gain twist rifling. Seems to me that type of rifling has some significant advantages to conventional rifling. Any comments on the most appropriate rate of twist gain would also be useful.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/26/2017 at 14:49
koshkin View Drop Down
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Are there many modern barrels with gain twist? I thought it was an old idea that did not pan out, but with new machines it might be coming back.

However, I can not think of any modern guns with gain twist barrels aside from S&W 460 revolver.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/26/2017 at 14:55
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Bartlein makes a gain twist barrel.  If I were reloading, I would probably have one on a couple of my rifles.  Since I don't reload, it would not provide any advantage for me.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/27/2017 at 12:50
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I've heard the claimed advantages, and not sure how much is truth vs theory. I've never tried gain twist, so have no basis for comparison. I've never been dissatisfied with the performance I get from just selecting an appropriate conventional twist from a reputable precision barrel maker.

One definite disadvantage to it is on the manufacturing side of things. It can only be produced by cut rifling, not button rifling or hammer forging, so this limits the number of suppliers who can offer it, Bartlein being one of them since they use the single point cut rifling process.

I don't know how much of an issue it really is, but it seems to me that gain twist would cause "smearing" of the rifling grooves on the bullet as the twist is progressively getting tighter. It must not be a problem for bullet integrity or flight, but I don't see how that wouldn't weaken jackets and have a detrimental effect on flight drag to have widened, disrupted engraving marks on the bullet.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/29/2017 at 07:46
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I have had a few in .338 and I 1 in .408 I believe the Arisaka is also gain twist and everyone I have ever had no issues in grouping. I was able to load them hotter or use more powder and saw a significant increase in velocity (due to powder charge, not due to the twist) and not lose tightness of group as the progressive or gain twist is designed for this very thing. I think Shoyen (maybe Schon) or Shalk and Pope have documentation on this...

The Arisaka is a heck of a barrel very very good for its time and superbly accurate...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/29/2017 at 09:10
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Mike Rock claims he has done gain twist for a long time.  I read an article or something about it once.  His is just a fixed setup, you could not order whatever you want like Bartlein can do. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/30/2017 at 21:02
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With high velocity, modern cartridges, and jacketed bullets, the only advantage of gain twist rifling would be longer life of the barrel because of somewhat slower erosion in front of the chamber. Also, gain twist rifling would allow shooting very long and heavy bullets for any given caliber, like 260 grain bullets in .30 or such. That is because such bullets would need a very fast twist to stabilize, but a very fast twist near the chamber would wear out fast and would increase pressures. The Italians used gain twist in their Carcano rifles, which were very accurate and shoot long heavy .264" 160 grain  grain bullets which were stable to long distances, and with long barrel life. 

The real advantage of gain twist rifling, if properly calculated and made  for a caliber and bullet, is when shooting jacket-less lead alloy bullets. These bullets are softer and often get smacked and deformed when they start and hit and engage the rifling. A slower twist near the chamber helps these bullets ease into the rifling and a faster twist near the muzzle will stabilize them.  The trick with lead bullets is to send them out without abusing and deforming them while they travel between chamber and muzzle. I have such a barrel on a target cast bullet rifle and it is beyond amazing how accurate it is.
I would not spend money on gain twist for a .308 Win or such. 
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