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Left-Hand Gain Twist

MarkLeupold

On board the .25 train
Full Member
Minuteman
Feb 10, 2017
557
369
I listened to one of the podcasts today (Episode 171, I think) and a couple questions popped up in my head about LH-GT barrels.

What benefit is provided by gain twist if you are already are adequately stabilizing your preferred bullet and have no need to twist anything faster? I know Frank mentioned something about the barrels being really tolerant of different bullets/loads, but I wondered if that was a common assessment across multiple barrels and users?

Secondly, left hand twist and gain twist are used by Frank as a pairing. There is almost no time where he says one and doesn't reference the other with it. I do know that they are mutually exclusive, but I want to make sure I'm getting it right. The left hand twist gives the cancelling spin drift/Coriolis and gives the modified recoil pulse or does the gain twist also contribute to the different recoil pulse?

Thanks for the clarification!
 
I think that the benefits of gain twist are still being determined and explored. But from some things I’ve read, it seems that it would allow you to start with a slower twist than current and finish up in the same place. Well, what difference does that make? Does it allow you to push them faster? Does it make it more forgiving for a wider range of bullet weights? Does it allow you to use your favorite load and get more barrel life?

I think the potential is interesting enough to explore with my next barrel.
 
I think that the benefits of gain twist are still being determined and explored. But from some things I’ve read, it seems that it would allow you to start with a slower twist than current and finish up in the same place. Well, what difference does that make? Does it allow you to push them faster? Does it make it more forgiving for a wider range of bullet weights? Does it allow you to use your favorite load and get more barrel life?

I think the potential is interesting enough to explore with my next barrel.

I'd like to explore it too, and while I'm still very early in my current barrel and see it lasting me at least two or three years, I still plan on my next one being a LH-GT either for the benefits of it, or for the experimentation.
 
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My LH-GT was my most accurate rifle.it was 6.5x47..i would probably do it again..i wouldn't recommend LH for bigger cal or magnum..recoil is on stock whip opposite direction meaning..towards your face
 
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I listened to one of the podcasts today (Episode 171, I think) and a couple questions popped up in my head about LH-GT barrels.

What benefit is provided by gain twist if you are already are adequately stabilizing your preferred bullet and have no need to twist anything faster? I know Frank mentioned something about the barrels being really tolerant of different bullets/loads, but I wondered if that was a common assessment across multiple barrels and users?

Secondly, left hand twist and gain twist are used by Frank as a pairing. There is almost no time where he says one and doesn't reference the other with it. I do know that they are mutually exclusive, but I want to make sure I'm getting it right. The left hand twist gives the cancelling spin drift/Coriolis and gives the modified recoil pulse or does the gain twist also contribute to the different recoil pulse?

Thanks for the clarification!
LH twist mitigates spin drift, not coriolis (which is generally over calculated by most BC calculators). Remember, (to be succinct) coriolis is the effect of the planet moving, and the direction you're shooting, and where the bullet will land/strike because of perception of where the target is when sent, and where the target will be, due to planetary mechanics, when it lands/strikes; LH or GT rifling has no direct effect on those variables, spin drift does (or the negation of the spin drift to be accurate). LH twist also allows the torque that occurs, as the rifle recoils, to torque into your body (assuming right handed shooter here) versus torquing the rifle away from the shooter with a RH twist. Pope did a lot of this experimentation over a hundred years ago, using anecdotal evidence, without truly understanding why. Regardless, he was on the right track.

The Gain Twist allows better use of bullets across a range because it limits the deformation of the bullet as it enters the lands and grooves. A static twist rate is optimized for one length of bullet (not weight, but length) so that it stabilizes the bullet, but also doesn't deform it. The GT allows different bullets (of different lengths) to be used so that deformation is limited, which equates to better accuracy down range (at distance). Deformation occurs, and is more prominent, when long for caliber bullets are used (which is the trend these days in our sport), and when the front of the bullet begins to turn upon hitting the lands/grooves, but the rear of the bullet wants to keep going straight forward ("An object in motion tends to stay in motion until affected by an outside force"; this is the opposite of that, in that a "An object at rest will stay at rest until acted upon by an outside force). As the rear of the bullet remains (from a rotation perspective) at rest, the front beings to turn, and thus deforms the bullet (jacket separation, core deformation, etc.), so when it leaves the barrel, it is no longer a uniform projectile. This non-uniform bullet then tends to oscillate ("wobble") as it spins and leaves the muzzle. This oscillation normalizes, and then worsens (bullet becomes less stable) as range increases and spin rate decrease. Hence why this is seen more at distance than up close. This oscillation also inhibits the time it takes to stabilize/normalize just after it leaves the muzzle, so you're "optimum" BC is effective for a shorter part of the bullets Time of Flight (and is generally lower than if the projectile was not deformed), since at best, we often just average a BC for ballistic calculations (even multiple BC calculations methods are still an average, just at more points along the arc).

While both are mutually exclusive options, it only makes sense to do both these days, since the mark up for the "odd" rifling or GT will be there, regardless of whether one or the other, or both, are requested. Might as well just order a bbl blank with both, unless you're in the southern hemisphere. In which case, a RH GT barrel may make more sense (from a spin drift cancellation perspective).
 
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This has been bugging me.

Right hand twist causes spin drift to the right. Wouldn't alert hand twist barrel just shift it to the left. How is their spin drift with Rh but less or none to with LH?
 
Yes, left hand twist causes spin drift to the left. However, while the magnitude is small everywhere I’ve shot, the Coriolis Effect will still pull the bullet to the right in the northern hemisphere. On the whole, you’ll end up say 0.6mrad left instead of 0.8mrad right in zero wind at 1000yd.
 
Yes, left hand twist causes spin drift to the left. However, while the magnitude is small everywhere I’ve shot, the Coriolis Effect will still pull the bullet to the right in the northern hemisphere. On the whole, you’ll end up say 0.6mrad left instead of 0.8mrad right in zero wind at 1000yd.

Ok this blanket statement makes no sense to me either. Doesn't the Coriolis effect change depending on firing azimuth? How does left hand twist universally help cancel it?
 
Ok this blanket statement makes no sense to me either. Doesn't the Coriolis effect change depending on firing azimuth? How does left hand twist universally help cancel it?
You are correct. I think @gnochi is confused between spin drift and coriolis. There are quite a few that fall into that group...
 
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You are correct. I think @gnochi is confused between spin drift and coriolis. There are quite a few that fall into that group...

Coriolis Effect vertical component: which direction you shoot impacts how high or low your shots drift.

Coriolis Effect horizontal component: your shots drift further right as you go further north of the equator.

Spin drift: your shots drift more right the faster the bullet is spinning with a right-hand twist (and the more the bullet is imbalanced, etc.)

So, if you have say an 8 twist 6.5 Creedmoor and you’re at 45deg North, at 1000yd you might have 0.7mrad of spin drift and 0.1mrad of Coriolis horizontal drift to the right. With a right hand twist, they add to each other - 0.7mrad right spin and 0.1mrad right Coriolis results in 0.8mrad total right drift. With a left hand twist, they subtract from each other - 0.7mrad left spin and 0.1mrad right Coriolis results in 0.6mrad total left drift.

Is the magnitude huge? No, and we know how to account for it. But it exists, and negating factors is more optimal than stacking them.

There are also impacts on how the rifle torques into vs away from you that are probably more immediately noticeable.

cc @newguy2k3v2
 
Coriolis Effect vertical component: which direction you shoot impacts how high or low your shots drift.

Coriolis Effect horizontal component: your shots drift further right as you go further north of the equator.

Spin drift: your shots drift more right the faster the bullet is spinning with a right-hand twist (and the more the bullet is imbalanced, etc.)

So, if you have say an 8 twist 6.5 Creedmoor and you’re at 45deg North, at 1000yd you might have 0.7mrad of spin drift and 0.1mrad of Coriolis horizontal drift to the right. With a right hand twist, they add to each other - 0.7mrad right spin and 0.1mrad right Coriolis results in 0.8mrad total right drift. With a left hand twist, they subtract from each other - 0.7mrad left spin and 0.1mrad right Coriolis results in 0.6mrad total left drift.

Is the magnitude huge? No, and we know how to account for it. But it exists, and negating factors is more optimal than stacking them.

There are also impacts on how the rifle torques into vs away from you that are probably more immediately noticeable.

cc @newguy2k3v2

Ok yes Coriolis effect on elevation depends on your azimuth. How then does the bullet drift right on the horizontal regardless of azimuth?
 
Ok yes Coriolis effect on elevation depends on your azimuth. How then does the bullet drift right on the horizontal regardless of azimuth?

The Earth is a sphere but spins on an axis. Bullets and other ballistic objects want to follow a great-circle route (full diameter, not partial slice), but because the earth is spinning, that great-circle route is instantaneously changing as the object travels unless you’re at the equator. If you’re in the Northern Hemisphere, the instantaneous great circle route will be slightly to the right of the previous one, and in the Southern Hemisphere it will be slightly to the left. The way the math works, it ends up being based on your latitude.
 
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Coriolis Effect vertical component: which direction you shoot impacts how high or low your shots drift.

This isn't actually Coriolis - it's Eotvos. https://en.wikipedia.org/wiki/Eötvös_effect

Coriolis Effect horizontal component: your shots drift further right as you go further north of the equator.

Spin drift: your shots drift more right the faster the bullet is spinning with a right-hand twist (and the more the bullet is imbalanced, etc.)

Spin drift is actually a minor manifestation of the Magnus effect, if I understand things correctly - https://en.m.wikipedia.org/wiki/Magnus_effect - and Magnus also has an explanation for aerodynamic jump. Either way, as far as spin drift is concerned, the bullet will drift ever so slightly in the direction of the twist. Slightly right for a right hand twist barrel, slightly left for a lefthand twist barrel.

So, if you have say an 8 twist 6.5 Creedmoor and you’re at 45deg North, at 1000yd you might have 0.7mrad of spin drift and 0.1mrad of Coriolis horizontal drift to the right. With a right hand twist, they add to each other - 0.7mrad right spin and 0.1mrad right Coriolis results in 0.8mrad total right drift. With a left hand twist, they subtract from each other - 0.7mrad left spin and 0.1mrad right Coriolis results in 0.6mrad total left drift.

That's an awful lot of spin drift. I just ran numbers on a 140 Berger Hybrid fired at 2820fps in an 8 twist barrel with LH rifling using AB Mobile at a distance of 1000 yards. With wind set to 0, and Coriolis and Spin drift turned off, I get 0 wind correction. Coriolis turned on, spin drift off, I get .1L (ie, as expected, in the northern hemisphere, the bullet drifts slightly to the right due to Coriolis). Coriolis on, spin drift on, I get .1R (so, spin drift is worth .2 mils at 1000).

If I reverse the twist rate, I get .1L with Coriolis only, and .2L with spin drift added in. Why? Because of rounding error - so spin drift is really less than two full tenths - and the math in the app is choosing to round up with the left twist situation, and down with the right twist situation (for whatever reason).

.7 mills at 1000 yards is a huge amount of spin drift...

There are also impacts on how the rifle torques into vs away from you that are probably more immediately noticeable.

I've got a LH GT barrel (12 to 8). I don't notice any difference in recoil profile between it and my 8-twist RH barrel. What I do notice is that I can push the loads harder, with more resultant velocity, before I see pressure signs. It might just be a faster barrel, too, but it seems like the slower starting twist allows pressure to build a little more gradually? That's about it. The barrel doesn't just magically shoot everything I feed it, as some have implied, but it does seem to group everything (even the stuff way outside a node) inside 3/4 MOA. Best groups so far are in the 1/4 MOA size, which is probably a shooter limitation and not equipment...
 
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Thank you for the correction on Magnus and Eotvos effects. I certainly won’t be the person to state that a 3dof calculator (iSnipe) is both accurate and handling inputs correctly, but that’s where I pulled the numbers from, and at least the right hand twist number corresponds correctly to my 1000yd DOPE.

I do look forward to using the 10-6 LHGT in 300PRC that I’ll have later this year For Science!
 
Spin drift is actually a minor manifestation of the Magnus effect, if I understand things correctly

All right, I was tired when I wrote that yesterday - it's not correct. It's a gyroscopic effect, called "yaw of repose" - Litz even refers to it as gyroscopic drift. That doesn't change how the phenomenon manifests - the bullet still drifts slightly in the direction of the twist.

BTW - this Wikipedia page seems to be pretty complete... https://en.wikipedia.org/wiki/External_ballistics
 
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Frank has mentioned at times in the podcast how the LH gain twist allows the rifle to torque into the shoulder a bit as a RH shooter, which is nice. My gut says that's a minor effect, though, and a LH shooter wouldn't necessarily be better off with a RH gain twist just on that one effect. Does that make sense?

A also plan on a gain twist for my next barrel, and despite being a lefty I'd probably go with LH gain twist.
 
You guys sure know how to overcomplicate shooting.

If you are curious, buy a LH twist barrel and check it out for yourself, and see what actual benefits there are that you can perceive.

All this round about talk about Otvos, Magnus, Coriolis, spin drift, etc effects isn't going to amount to fuck all at the firing line. If you are on the firing line and thinking about all that prior to pulling the trigger, you may as well pack it up and go home.
 
The benefits on paper do seem pretty interesting..... but in practice I really doubt the average guy can warrant spending extra money on a barrel like this over an extra case of ammo and some more trigger time learning how to call the wind.
 
A mix of all three posts above

alot of lefties shoot and have shot "right handed" rifles using their left shoulder

if all the L/R twist was true the lefties would be winning every match and own every record since the inception of rifling

how about just learn your weapon, take notes and read the wind
 
The benefits on paper do seem pretty interesting..... but in practice I really doubt the average guy can warrant spending extra money on a barrel like this over an extra case of ammo and some more trigger time learning how to call the wind.

I actually didn't see much of an upcharge for the LH GT barrel I got from MHS, so I'm not sure that is a really big deal. I mean, when you're getting a barreled action set up a few dollars more for the LH GT is lost in the noise.

As far as all the benefits, the one I have seen most is just the forgiveness it has with different bullets...it seems to shoot everything well.
 
A light gain twist (say, from 8 to 7 - just 1 inch of gain) isn't super expensive. I forget how much I was told, but I'm thinking it was $50 or less? Judging by MHS's pricing, it might be no charge. For any more gain, they charge $160.

LH vs RH is no additional charge.

I decided to play around, and ordered a 12-8 LH GT barrel for my 6.5 Creedmoor. The biggest difference I've noted is that the barrel basically doesn't foul. It cleans so easily, it's almost scary. It's a bit faster than my previous barrel, but it's also 2" longer, so that's likely a wash. It shoots everything 3/4 MOA, but it's not some magic half-MOA thing. It definitely prefers 147gr ELD-Ms, shooting them into a bughole at 200y when I do my job.

The cleaning benefit is nice, but honestly, I got similar accuracy from my 1:8 RH non-GT Bartlein (everything into sub 3/4 MOA, with the best stuff shooting 3/8 MOA). I likely wouldn't spend the extra cash on a "radical GT" barrel (as Bartlein calls it) in the future.
 
I am up to 6 LH GT Barrels in various configurations, the latest my MHSA Valkyrie build is one of them.

The Pros:

1. Decreased Load Pressure
2. Increase results with a variety of bullet weights
3. Solid Speeds

In terms of the SD/CE/AJ/ Magnus/Evotos effects, think about it this way, every error we induce including these drifts go to the right in varying degrees, (PS, SD is only 1.25% of your elevation so you should really not be dialing it under 10 mils) to include the shooter errors with a right handed shooter. So why continue to compound these errors when you can mechanically subtract them with no effort on your part. So spinning everything to counter these factors makes more sense.

The only reason we shoot right hand twist barrels today is the machines that mass produce this stuff was designed to turn right. Many rifles prior to the turn of the century had LH twist barrels.

So you are cancelling out a percentage of the right hand errors.

In terms of shooter recoil, you can feel it at first especially if you are off you belly. In the prone not so much, but the idea of the LH GT which came from Pope, and the Pope Sharps rifles were designed for Silhouette competition. He record in this regard lasted 47 years or so. 47 years to beat a turn of the century competition record. He stated that for a right handed shooter, in order to keep the rifle on target when standing offhand shooting steel pigs and chickens, you wanted a LH Twist rifle and he gained it to keep the pressure curve consistent.

The barrels work, and work great, I have not seen any negatives and only positive results coming from my Bartlein LH GT Barrels.

Hope that answers some of this as I believe in them 100%
 
700 rounds into my first LHGT bartlien 6.5 CM
My observations;
Easy to develop a load with any bullet I tried.
Factory loads slightly more accurate than in other barrels I’ve had
More accurate wind calls when shooting this rifle
Did not notice the effects from rifle torque until I went back to a short 308 in same stock. Then it felt like gun was trying to twist away from me and very noticeable difference in sight picture during/after recoil. This difference in rifle behavior is much more noticeable from tripod barricade and less supported positions.

Hard to say if performance gains are all due to rifle or what’s attributable to my fundamentals. I do notice other platforms I have similar results to what I’ve always had. I think all positive attributes of LHGT would be more evident with larger recaoiling rounds at longer ELR. distances.

If LHGT is an option I will continue to use in the future. Not a big enough difference to force any barrels into early retirement.

I will continue to train with a short 308 as it exploits any weakness in fundamentals.

One mans experience your mileage may vary.?
 
can you elaborate: "More accurate wind calls when shooting this rifle"

less drift per MPH of wind?
smaller group size left to right in same conditions?

thanks
brian
 
Is there any sort of standard on the gain twist?
No. You could get pretty much anything you want. However, Bartlein recommended nothing more than a one inch change for standard lead core projectiles.

For example:

.264 Barrel 8.75-7.75:1 Twist

.308 Barrel 10-9:1 Twist.
 
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Frank Green recommends about 3/4 inch twist gain as normal. Anything else is considered extreme GT.
No. You could get pretty much anything you want. However, Bartlein recommended nothing more than a one inch change for standard lead core projectiles.

For example:

.264 Barrel 8.75-7.75:1 Twist

.308 Barrel 10-9:1 Twist.
Thank you both.
 
I was at Camp Perry, OH during the CMP national championships and I spoke to Joseph Carlos of Magnum Loading Service.
He builds and sells AR-15 service rifles with (Bartlein) gain twist barrels. He is using a pretty radical change, I believe it was 13 to 6 or 13 - 7. Basically he said he wants to double the twist rate over the length of the 20" barrel.

His uppers are purpose built to run the Berger and Sierra 90gr bullets loaded long for single loading in the slow fire stages from 600yds out to 1000yds.

The best thing about his uppers though is that even though they are throated for the 90's and shoot them very well, they still shoot the 69/77gr loads well at mag length for the rapid fire portions at 200/300yds. Most rifles with constant twist rates that are throated for the 90's do not perform very well with the mag length loads.

So, while for most folks on the 'Hide where we find a single load/bullet and stick with that, these gain twist service rifle uppers can easily accommodate long line loads and not sacrifice performance at any yardage.
 
Reached out to Mile High this week about getting a LH Gain twist barrel for 300WM to shoot from 190gr SMK up to 230gr Bergers. Was advised that the recoil of the 230gr Bergers would be hell on my face with the gun recoiling in to me.. lighter shooting calibers it was no big deal... Has anyone experienced this unintended consequence with magnum rifles and LH twist barrels ?
 
Reached out to Mile High this week about getting a LH Gain twist barrel for 300WM to shoot from 190gr SMK up to 230gr Bergers. Was advised that the recoil of the 230gr Bergers would be hell on my face with the gun recoiling in to me.. lighter shooting calibers it was no big deal... Has anyone experienced this unintended consequence with magnum rifles and LH twist barrels ?

Ask a lefty shooter if recoil to the face is hell....I personally don’t think you have anything to worry about. Shooting a 230 out of a 300win is going to have recoil regardless of what way the twist is going.
 
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Ask a lefty shooter if recoil to the face is hell....I personally don’t think you have anything to worry about. Shooting a 230 out of a 300win is going to have recoil regardless of what way the twist is going.
Valid point.... maybe I should just shoot my rifle left handed with my right hand twist rifle and see what happens.. hummm
 
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This concept always intrigued me. How extreme can you get?

50:1 - 7.75:1?

Does it matter what starting is as long as exit isnt more than a jacketed bullet can handle?
 
Yes that was bad advice

Who told you that ?

You cannot over, over twist it, less is better,

I have a 13-5 338 that uses a specific bullet, if you tried shooting a jacketed bullet out of this barrel the bullet would rip apart
 
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Reached out to Mile High this week about getting a LH Gain twist barrel for 300WM to shoot from 190gr SMK up to 230gr Bergers. Was advised that the recoil of the 230gr Bergers would be hell on my face with the gun recoiling in to me.. lighter shooting calibers it was no big deal... Has anyone experienced this unintended consequence with magnum rifles and LH twist barrels ?
Yes that was bad advice

Who told you that ?


Mike at Mile High..

" You might want to consider a RHGT, Otherwise your gonna take that recoil on the chin. LHGT is good for smaller calibers. Just a thought"

Just did not know if anyone else had similar feelings or opinions
 
If you had to choose between the 2, which would be more helpful, gain twist or left hand twist? Im looking for a 6mm LHGT and I can’t find a blank in both. I can find one or the other.
 
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GT would be my thought. The LH twist helps with recoil management and countering spin drift (in certain circumstances). However, the GT helps limit bullet deformation when shooting "high BC for caliber" bullets. If it were me, I'd opt for the increased accuracy (because those bullets aren't being deformed as badly), over the recoil management issues. Recoil management can be trained, bullet deformation is physics. You ain't changing physics with training....
 
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big difference between the two

with the Gain Twist, the bullet is treated much better like noted above, as well the load is not as picky in terms of weight,

I am up to 6 of these, can't overstate how great they work
 
So if you had to pick between the 2 which way would you go, if you didn’t want to wait 6 months straight from Bartlein to get left hand and gain?
 
Anyone know where to buy savage pre fits with gain twist?
 
I use a Left-Hand Gain Twist

And not just a Left-Hand Twist,

Mark Chanlin here in CO who been making barrels forever does strictly LH twist on certain calibers, but I am not just defaulting to a LH Twist, I am using both together

One without the other will not do anything negative, but pairing both together is the smart play for people in the US