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Gain Twist rifling...does it work

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William Metford's gain twist rifling was used on long range match rifles (ML & BL); so was Rigby's uniform twist rifling. As 52Bore notes above neither shot any better of worse than the other. I've won long range matches with a Metford and been beaten by others with uniform twist. One theoretical advantage was that the wrap on paper patched bullets was sheared better enabling it to fall away from the bullet as it left the barrel. Can't say I have noticed any difference though.

David
 
Some very accurate rifles have been built with gain-twist barrels, but that form of rifling has never been demonstrated to have any real advantage in potential accuracy over fixed-pitch rifling suited to the projectile and velocity. The most intense efforts to develop extreme accuracy have been lavished on modern benchrest rifles, and every known variant of rifling geometry has been tried exhaustively. If gain-twist rifled barrels showed the slightest advantage in accuracy, you may be sure that benchrest shooters would be using them: they aren't.
There are some mechanical characteristics of gain-twist rifling which are not commonly discussed or widely understood:
1. It is not possible to lap a gain-twist barrel by conventional means to remove or mitigate tool marks or other irregularities left in the bore by the reaming and rifling processes.
2. It is not currently possible to rifle a gain-twist barrel by other than conventional cut-rifling, so far as has been reported.
3. The width of the lands and grooves in the gain-twist barrel varies with the change in pitch, because of the change in aspect of the cutter as it progresses through the barrel; this results in wider grooves and narrower lands at the breech than at the muzzle, so that the surface of the projectile is continually deformed both as to pitch and land/groove width as it progresses through the bore. The stresses placed on the surface material of the projectile are shearing stresses for the full length of travel through the bore.
Harry Pope was, perhaps, the greatest proponent of the gain-twist system for use with his highest development in lead-bullet accuracy: the breech-muzzleloading rifles he built and which were justly renowned for superior accuracy. However, on reflection, it seems obvious that engraving a soft lead alloy bullet with the fastest pitch at the muzzle, forcing it all the way through the bore to the breech (and continually changing the geometry of the engraving on the bullet body by shearing force), and then reversing the process in firing the bullet must be less than optimal mechanically. In fact, I have always believed that the demonstrated superiority of Pope's rifles was due to the superior level of workmanship he put into his barrels and the rifles he built, and that rifles made by him with fixed-pitch rifling would have been just as accurate. It is a matter of record that he built some heavy barrels with fixed-pitch rifling for use with the International Match 1903 rifles, and that they were among the best in accuracy testing.
In summary, then, gain-twist rifling can result in excellent rifle accuracy, but not better than conventional, fixed-pitch rifling, and there are some real factors which weigh against the gain-twist for common use in rifles.

mhb - MIke - barrel maker, retired
 
This has been one of the more interesting threads posted here to my mind. What I come away with is you can spend extra money on a gain twist for the bragging rights and shoot as well as the guy with standard twist especially when dealing with muzzle loaders.
 
IF you take a gander at The Muzzle-Loading Cap Lock Rifle by Ned Roberts, you will see I think more advantage when using a "tapered bore" than a gain-twist. A tapered bore actually constricts around the bullet a few inches before it reaches the muzzle. The bullet being very snug when loaded, after descending a few inches, is then easier to load. When fired the base of the bullet upsets.., and so grabs onto the lands and grooves. As it nears the muzzle the seal is further improved. Roberts (iirc) was using paper patched, muzzleloading conical bullets, and (iirc) it was used by almost all of the champion shooters of his era. They were shooting at least 220 yards (40 rods) and farther.

LD
Actually what you have described is a CHOKED bore. A TAPERED bore reduces in diameter uniformly from breech to muzzle. This taper is on the order of half a thousandth of an inch in the length of the barrel. Harry Pope made his barrels with gain twist (about a quarter turn in the length of the barrel) and a tapered bore. He was making bullet barrels and not round ball barrels.
 
The only thing I can say for sure about gain twist is that it gives accuracy comparable to uniform twist barrels. If the opposite is done - rifling that slows to any degree toward the muzzle - any hope of accuracy goes out the window.
 
The only thing I can say for sure about gain twist is that it gives accuracy comparable to uniform twist barrels. If the opposite is done - rifling that slows to any degree toward the muzzle - any hope of accuracy goes out the window.

I would agree to the extent that a gain-twist barrel CAN give accuracy comparable to fixed-pitch barrels, but would note that, for reasons mentioned earlier, it is more difficult to make a really excellent gain-twist barrel than a fixed-pitch one, or to achieve top accuracy from one because the gain-pitch is harder on the bullet's geometry as delivered at the muzzle.
I will caveat these statements, too, as applicable to elongated projectiles, specifically - I am not at all sure that a patched roundball is sensitive to changes in pitch to the same extent, or would suffer much from slight slowing at or near the muzzle, so long as the resulting rotational speed is sufficient to stabilize the ball.
It may also be of interest to note that button-rifled barrels, long noted for excellent internal finish (when properly made), and top-level accuracy (if made by one of best makers, such as Shilen), WILL exhibit small variations in pitch from end-to-end. That is because the rotation of the button on its passage through the bore is affected by variations in hardness of the barrel material (unavoidable), and the fact that the forces on the button and the barrel steel are so great that there is no way to effectively control its rotation to prevent such minor deviations. In spite of this, excellent barrels are made by button-rifling, and match winning rifles assembled with them.

mhb - MIke
 
Thank you gentlemen! This has been very useful to me, as a gun building project begins to take firmer shape. It began with a 38" gain twist barrel already in hand. But that barrel is four inches longer than the barrel and gun I want to copy, and it is swamped, whereas the copy gun's barrel is slightly tapered on the exterior. I did not want to give up the benefits of gain twist if I ordered a replacement 34" barrel, and so it got me wondering...and I do have two British sporting rifles that have it. Both of those rifles are from the 1880s, have gain twist and tapered bores. They are incredibly accurate guns. So, it got me wondering. Is gain twist something I should get if I can, when I can, or should I forego it...wondering what the down side could be...
 
I would agree to the extent that a gain-twist barrel CAN give accuracy comparable to fixed-pitch barrels, but would note that, for reasons mentioned earlier, it is more difficult to make a really excellent gain-twist barrel than a fixed-pitch one, or to achieve top accuracy from one because the gain-pitch is harder on the bullet's geometry as delivered at the muzzle.
I will caveat these statements, too, as applicable to elongated projectiles, specifically - I am not at all sure that a patched roundball is sensitive to changes in pitch to the same extent, or would suffer much from slight slowing at or near the muzzle, so long as the resulting rotational speed is sufficient to stabilize the ball.
It may also be of interest to note that button-rifled barrels, long noted for excellent internal finish (when properly made), and top-level accuracy (if made by one of best makers, such as Shilen), WILL exhibit small variations in pitch from end-to-end. That is because the rotation of the button on its passage through the bore is affected by variations in hardness of the barrel material (unavoidable), and the fact that the forces on the button and the barrel steel are so great that there is no way to effectively control its rotation to prevent such minor deviations. In spite of this, excellent barrels are made by button-rifling, and match winning rifles assembled with them.

mhb - MIke
Mike, all informative, thank you. This rifle building project started out needing a barrel shooting patched round balls. Eventually I arrived at the idea that, forced to make a choice, conicals would be preferable. They (longer) are definitely more sensitive to twist rates. I am using Colerain, which makes a lot of barrels for a lot of shooters, including gain twist, and so far I have not heard anything negative. So, I am confused, basically, because Scott Keller at Colerain asked if I wanted a happy medium gain twist that will work with both conicals and PRBs...
 
Mike, all informative, thank you. This rifle building project started out needing a barrel shooting patched round balls. Eventually I arrived at the idea that, forced to make a choice, conicals would be preferable. They (longer) are definitely more sensitive to twist rates. I am using Colerain, which makes a lot of barrels for a lot of shooters, including gain twist, and so far I have not heard anything negative. So, I am confused, basically, because Scott Keller at Colerain asked if I wanted a happy medium gain twist that will work with both conicals and PRBs...

What I don't want to do is add confusion to your project. I'm sure Colerain can make a barrel which will give you the results you want. However, you need to coordinate your intentions with Colerain, so that he understands what weight, caliber and design of conical you want to shoot. It would be much easier to achieve a good compromise gain pitch for a patched roundball or patched picket, than for the patched roundball and a naked maxi or other bullet with long bearing surface and of significantly greater weight than the RB. All my ML/BP bullet guns have fixed pitch rifling, and I shoot pickets, minies, maxi-types and long, heavy bullets in various models of rifle appropriate to the bullet type, with excellent accuracy, but only RB and pickets or, occasionally, maxis, can be made to shoot about equally well in the same rifle, in my experience.
Good luck!

mhb - MIke
 
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What I don't want to do is add confusion to your project. I'm sure Colerain can make a barrel which will give you the results you want. However, you need to coordinate your intentions with Colerain, so that he understands what weight, caliber and design of conical you want to shoot. It would be much easier to achieve a good compromise gain pitch for a patched roundball or patched picket, than for the patched roundball and a naked maxi or other bullet with long bearing surface and of significantly greater weight than the RB. All my ML/BP bullet guns have fixed pitch rifling, and I shoot pickets, minies, maxi-types and long, heavy bullets in various models of rifle appropriate to the bullet type, with excellent accuracy, but only RB and pickets or, occasionally, maxis, can be made to shoot about equally well in the same rifle, in my experience.
Good luck!

mhb - MIke
Thanks Mike. Your posts are really helpful. This is why, after a long conversation with him, I recently gave Scott (Colerain) my trade-off preference: If it must be one or the other, I prefer a tighter turn rate so longer (heavier) bullets can be confidently shot with accuracy. The goal with the .62 percussion rifle is to go after elk, bear, as well as early deer here in PA, so why not have it shoot longer bullets and be even more effective, as effective as it can be. The guys here have been very helpful and kind.
 
F.W. Mann's book 'The Bullets Flight from Powder to Target' 1909 can be downloaded at https://duienforcers.wildapricot.org/Re ... o_1909.pdf
Raedwald, thank you. Having the URL spoon-fed to me is inexcusably easy, and had I seen your post earlier, i would have read the Mann book earlier. I just discovered your post this morning and I am now drinking coffee and reading Mann's book. So far it reminds me of the various British military committees of the 1840s-1880s, who held open competitions among the great gun makers of their day. Lancaster, Holland, Alex Henry, Gibbs, Purdey, Westley Richards, Rigby etc. all competed at one match or another, using their own proprietary rifling and ignition systems. Then the British officers would sit back, along with the sporting press, and engage in both impressive technical analysis and humorous conjecture about the results. Most of the British black powder sporting rifles (muzzle loading and breech-loading metallic cartridge) used both gain twist and tapered bores, and they showed no ill effects. Lancaster's smooth oval bore cannons used gain twist, and they were so successful that they were made a state secret for years. Anyhow, I will report back on the Mann book.
 
Dave,

The Enfield (P '53 family) has tapered rifling, and it probably Does help in keeping a seal. The bore in these is straight,(Parallel) but rifling is about 15 thou deep at breech, going to only .005 deep at muzzle.
 
OK, Mann (1907) was a fascinating read and a reminder to avoid complicated formulae whenever possible. Overall he was devoted to understanding more basic theories of shooting than twist rates. He does not address gain twist per se, but rather how bullets may or may not be affected by inertia and friction vis-a-vis the rifling; it means that he was dealing "slightly above conjecture" (his words). Mann deals with bullets "jumping/stripping the grooves" in a pretty basic mechanical way. All I can say is I am glad I read this book, thank you Coffin for recommending it and Raedwald for providing the URL. It seems to me that any answers to the gain twist question can only be found in the records of rifle barrel manufacturers who made or make gain twist rifling. More than anyone else, the British sporting rifle makers experimented with gain twist and other rifling variations. Most of the British gunmakers' records were thrown away or lost in German bombing, sadly, so unless someone at Purdey's or Holland are willing to pore over what they have in house, this subject is resolved only by the physical evidence the other makers left behind: Their gain twist barrels we now shoot so accurately. Several years ago, acting on a tip from writer Steve Helsley, I purchased the original Charles Lancaster patents from a book dealer in London. Perhaps I need to go back and re-read those, because Lancaster does discuss his rifling methods in his oval bore patent applications. He was a big believer in gain twist. Then again, his rifling was practically smooth and barely discernible to the eye, so gain twist might have a pronounced effect in his barrels. Mann has a formula for that, I am sure, but I have a headache from reading his book, and so I am going for one more cup of coffee and two more ibuprofen...
 
mann bore kinetics.jpg
barrel rifling rate formula from Mann.jpg
 
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Mann has a formula for that, I am sure, but I have a headache from reading his book, and so I am going for one more cup of coffee and two more ibuprofen...

Do you think TWO ibuprofen will be enough? ;)

mhb - MIke
 
Do you think TWO ibuprofen will be enough? ;)

mhb - MIke
You were right, two ibuprofen were not enough. Thank you for your helpful insights, Mike. Your own direct experience making barrels informs you well beyond what I can array. Some people are livin' the dream, I will remain livin' the gain twist mystery,,,
 
You were right, two ibuprofen were not enough. Thank you for your helpful insights, Mike. Your own direct experience making barrels informs you well beyond what I can array. Some people are livin' the dream, I will remain livin' the gain twist mystery,,,

Experience is always helpful in any field, and, as you venture into the gain-twist mystery, I hope you will share what you find.

mhb - MIke
 
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