Educate me on the advantage of a Gain twist rifling

[kelljp]

I've been building a rifle this winter and decided to bump the barrel up to a 54 cal ( 54s seem to shoot better). I've seen alot of discussions on the gain rifling. Can someone simplify the term ?

 

[leadhoarder]

It means that the rate of twist changes as it goes down the bore. The rate of twist increases as it travels down the bore.

 

[Wildrangeringreen]

The idea is that the bullet is subjected to less shearing force from the rifling spinning the projectile during the initial burst of acceleration it is subjected to upon firing, then as it fully engages the rifling, its RPM is increased gradually until it is stable once it leaves the barrel (this supposedly reduces deformation to the bullet). On a ML, this is supposed to reduce the likelihood of the projectile stripping from the rifling.

I feel that variable depth rifling would be more useful on a ML, but that's just me. The grooves being deeper at the breech and gradually becoming shallower towards the muzzle ensures that the rifling constantly has a tight grip on the bullet. It also has the advantage of swaging the bullet as it is fired, which makes it a little more consistent (in theory) than standard rifling.

A lot of the different ways to rifle a barrel are almost purely theoretical, the only thing that seems to be solidly backed by math is that a projectile of certain weight and dimensions requires a minimum RPM to be stable in flight. Some people have good success with Progressive rate, some have better results with variable depth, and some see no difference between them and standard rifling.

 

[ohio ramrod]

Many modern hi powered rifles have gain twist to allow for faster rotations . Most muzzle loading rifles do not require the advantages of gain twist since we are dealing with less torques . Some people believe every little advantage helps.but my self believe a standard twist will shoot better than I can.But a lot of the old time bench shooters used gain twists in their rifles

 

[dave951]

As stated, gain twist is a twist that gets faster as it goes toward the muzzle. In actual practice, it can be very accurate but..... it is extremely picky as to load. Get the load right and it's a wonderful thing. Stray but a little.......you'll be wishing for regular twist.

 

[kelljp]

Thanks for clearing that up all.
It appears the consensus is not to go down that rabbit hole with a muzzleloader.

 

[52Bore]

Thanks for clearing that up all.
It appears the consensus is not to go down that rabbit hole with a muzzleloader.

Just FYI- Gain Twist was created and utilized during the ML era of the Mid-1800’s.
George Gibbs combined with Wm. Metford’s shallow/rounded gain twist rifling in his rifles as the LR accuracy in arms continued. (photo). Paper patch bullets.
Gibbs is what we see today from Pedersoli- no gain twist though.

 

[LME]

The idea is that the bullet is subjected to less shearing force from the rifling spinning the projectile during the initial burst of acceleration it is subjected to upon firing, then as it fully engages the rifling, its RPM is increased gradually until it is stable once it leaves the barrel (this supposedly reduces deformation to the bullet). On a ML, this is supposed to reduce the likelihood of the projectile stripping from the rifling.

I feel that variable depth rifling would be more useful on a ML, but that's just me. The grooves being deeper at the breech and gradually becoming shallower towards the muzzle ensures that the rifling constantly has a tight grip on the bullet. It also has the advantage of swaging the bullet as it is fired, which makes it a little more consistent (in theory) than standard rifling.

A lot of the different ways to rifle a barrel are almost purely theoretical, the only thing that seems to be solidly backed by math is that a projectile of certain weight and dimensions requires a minimum RPM to be stable in flight. Some people have good success with Progressive rate, some have better results with variable depth, and some see no difference between them and standard rifling.

In black powder rifles a gain twist rifeling allows one to use heavier charges and still maintain accuracy. Modern powders in magnum rifles needs a slower rate of burn than blackpowder to get maximum velocity as it builds up more gasses to push the porjectile. I have always thought gain twist was moot in modern rifles?

 

[Wildrangeringreen]

In black powder rifles a gain twist rifeling allows one to use heavier charges and still maintain accuracy. Modern powders in magnum rifles needs a slower rate of burn than blackpowder to get maximum velocity as it builds up more gasses to push the porjectile. I have always thought gain twist was moot in modern rifles?

Never really have been any statistics compiled that demonstrate that it definitively does anything better than standard rifling, same as variable depth and Polygonal rifling (elliptical bores, round bottom/radiused rifling, modern 5-7R rifling) (least as far as I'm aware of). You can still use heavy charges in a BP rifle (or a smokeless rifle using Red Dot (which has a burn rate similar to 777)) with standard rifling, you just have to ensure that your projectile has enough bearing surface to hold onto the grooves. Just look at the BPE rifles, like the 577/500 BPE No. 2 (3-1/8"), which was often loaded with 165gr of BP and a 400gr bullet or .50-140-700 WCF (I know they're chamberings from after '65, but it is relevant). The guys selling gain-twist barrels claim it works miracles, but can't ever seem to back it up with anything; the guys that use gain-twists believe they do wonders, but often don't outshoot anyone else.

Gain twist is still offered by some barrel makers for modern guns, but much like historical shooters, people won competitions with standard rifling, variable depth, and gain twist. Just like in the 1800's, most modern shooters don't bother with it, as it is more finicky (and expensive to produce) than standard rifling, for no definite advantage. 1860 Colt's used gain-twist originally (it was the "wonder-tech" in rifling at the time, a product of the dawn of modern engineering/mathematics), yet new repro's don't, and they shoot just as well; and some target rifles used gain-twist, but some new repro's using standard rifling are shooting just as well in 800 and 1,000 yard comps. Much of the draw to gain-twist was based in the same logic James Forsyth was running with in his book: that a faster twist somehow drastically reduces the velocity and effectiveness of a projectile, due to excessive friction and the energy being changed from forward movement to rotation. That was mostly disproven by mathematics and trajectory studies in the 1840's and onward (ironically at the same time JF was making his claims), while you do lose some velocity from faster twists, we're talking 50fps or less, not the hundreds JF claimed.

Not to drag the thread into smokeless (which we're not really supposed to talk about), but modern smokeless rifle powder has been formulated to burn slower to allow us to produce more gas at the same pressures, to accelerate a bullet to much higher velocities without requiring a significantly stronger/heavier gun (that developed out of the experiments that began in Europe, Canada, and the US all the way back in the 1840's, trying to make a "better" gunpowder). That slower burning and lower pressure impulse also is what causes issues with bore-sized projectiles in SML's (not the topic of this forum). BP is honestly THE best powder for ML's, as the sudden high pressure impulse of that explosive upsets the bullet into the grooves very well, but it doesn't require gain twist to work well, even with high charges, so long as your projectile fit is proper.

So long as the RPM the bullet is spinning at once it leaves the barrel, it doesn't seem to matter how it gets there.

 

[LME]

Never really have been any statistics compiled that demonstrate that it definitively does anything better than standard rifling, same as variable depth and Polygonal rifling (elliptical bores, round bottom/radiused rifling, modern 5-7R rifling) (least as far as I'm aware of). You can still use heavy charges in a BP rifle (or a smokeless rifle using Red Dot (which has a burn rate similar to 777)) with standard rifling, you just have to ensure that your projectile has enough bearing surface to hold onto the grooves. Just look at the BPE rifles, like the 577/500 BPE No. 2 (3-1/8"), which was often loaded with 165gr of BP and a 400gr bullet or .50-140-700 WCF (I know they're chamberings from after '65, but it is relevant). The guys selling gain-twist barrels claim it works miracles, but can't ever seem to back it up with anything; the guys that use gain-twists believe they do wonders, but often don't outshoot anyone else.

Gain twist is still offered by some barrel makers for modern guns, but much like historical shooters, people won competitions with standard rifling, variable depth, and gain twist. Just like in the 1800's, most modern shooters don't bother with it, as it is more finicky (and expensive to produce) than standard rifling, for no definite advantage. 1860 Colt's used gain-twist originally (it was the "wonder-tech" in rifling at the time, a product of the dawn of modern engineering/mathematics), yet new repro's don't, and they shoot just as well; and some target rifles used gain-twist, but some new repro's using standard rifling are shooting just as well in 800 and 1,000 yard comps. Much of the draw to gain-twist was based in the same logic James Forsyth was running with in his book: that a faster twist somehow drastically reduces the velocity and effectiveness of a projectile, due to excessive friction and the energy being changed from forward movement to rotation. That was mostly disproven by mathematics and trajectory studies in the 1840's and onward (ironically at the same time JF was making his claims), while you do lose some velocity from faster twists, we're talking 50fps or less, not the hundreds JF claimed.

Not to drag the thread into smokeless (which we're not really supposed to talk about), but modern smokeless rifle powder has been formulated to burn slower to allow us to produce more gas at the same pressures, to accelerate a bullet to much higher velocities without requiring a significantly stronger/heavier gun (that developed out of the experiments that began in Europe, Canada, and the US all the way back in the 1840's, trying to make a "better" gunpowder). That slower burning and lower pressure impulse also is what causes issues with bore-sized projectiles in SML's (not the topic of this forum). BP is honestly THE best powder for ML's, as the sudden high pressure impulse of that explosive upsets the bullet into the grooves very well, but it doesn't require gain twist to work well, even with high charges, so long as your projectile fit is proper.

So long as the RPM the bullet is spinning at once it leaves the barrel, it doesn't seem to matter how it gets there.

I don't know how much gain twist helps if any but logic seems to say more rotations should be a benifit? more spin, more stability? black powder burns quick smokeless slow. It appears that getting a bullet starting to spin slow and increasing the farther down the barrel as it travels would allow one to use a larger charge. I haven't delved into this matter very deep as all my rifles are standard twist and are accurate and fast enough for my purpose.

 

[gun_painter]

Modern rifles using smokeless, and heavy for caliber bullets can reduce the peak pressures a bit using gain twist rifling. I know several shooters shooting the ELR (extreme long range) competitions that use gain twist to shoot out to 2 miles and beyond. They need fast twist rates to stabilize long bullets that defeat wind an drag well, but starting off with a fast twist will increase the chamber pressures by creating extra drag on the projectile.

I know this is a Blackpowder forum, and this doesn't really have it's place here, but on the extreme side of it, there have been very recent, and very interesting findings with extremely fast twist rates, and subsonic bullets.


In my opinion, which is less qualified to state that most of the folks here, gain twist on blackpowder rifles are a bit of a waste.

Branden