Gain twist barrels?

[Frank Green]

Let's have a separate thing on bullets in specifically the solids. One maker just recently made a comment to me....they feel the solids that the bullet should be with in about .0002" of the groove size on the barrel. Then they shoot better. Barrels with inconsistent bore sizes or sizes that are way bigger than the bullet etc...won't shoot the solids good. Then they hear complaining about the bullets don't shoot but shooters are running them thru factory barrels or barrels with bore sizes that are not even in the ball park.

Another group of shooters shooting muzzle loaders told us they won't even use brand Z barrels because they cannot get them to shoot with any consistency. They can feel the tight and loose spots in the bore as they push the bullet from muzzle to breech.

 

[tna9001]

Thank you for the insight, Frank!

 

[Raptorman2014]

Aren't rock creek barrels gain twist?

 

[bjay]

Aren't rock creek barrels gain twist?

My cheytac RC came with gain twist

 

[Jackomason]

Well I really have no say in ELR and I really only shoot 1200 and in but this post has got me thinking a few things. I must have heard wrong, but isn't the danger in over spinning a bullet that it won't want to leave it's original axis as opposed to following the trajectory path?

Would a change in twist compromise the bullets jacket? And at what point, only dramatic gain or would a difference of 2 be too much? my thought is that your slugging the barrel with a bullet, forcing the part of the jacket that contacts the lands to become thin and the part that contacts the groves to become tracks but then your changing the twist on those tracks... would that cause a tear in the thinner part?

And the last thought is: are these barrels reasonably priced? It's been said earlier that GT doesnt change the world but the can give you an edge, I know that if that edge is worth it or not is in the eye of the beholder but are there any definitive advantages to the average 1000 yard shooter?

I will say that the ability to shoot a wide range of bullet weights is interesting, there are a good amount of hunting calibers that would benefit.

Thanks guys, great read!

 

[cro789]

I just spoke with Mark from Bartlein and he advised me , for my application, a 23" .308 LH gain twist 11.5-11 5R barrel. This will go into my Desert Tech SRS A1. I am now waiting on my gunsmith to give me a call so I can order it. Mark also stated I should get between 3000 to 5000 rounds out of this set up. Sweet

 

[Lowlight]

Gain Twists do not compromise the jackets, they are not layered, they extend out so the bullet is not retracing the lines. This is a fallacy of GT Barrels that you increase the engraving on the bullet.

They protect the jacket more vs a standard twist that might be overly aggressive

They are not that much different from ordering a standard barrel, there is a small upcharge but if you are buying a custom barrel you are not gonna see it.

For an ELR Rifle going Left-Hand, Gaint Twist IS the right formula as you do not compound the drifts, but subtract them from each other.

 

[Nik S]

Fascinating stuff and thinking! --both the gain twist and the left twist for RH-shooter. I am earmarking both for my next rifle.

I'm especially intrigued with the potential for skid reduction on barrel entry--perhaps moreso than the potential to squeeze even more twist out of a barrel. It raises questions.

Does that initial skidding nick up the bullet? Will reducing skidding produce a cleaner bullet at muzzle with better ballistics in flight?

If that is true, there might be no velocity difference between a standard twist and a GT at muzzle, but would it make sense that a "cleaner exit" (EDIT: bullet is less marked up) from a GT barrel allowed a bullet to retain velocity longer over distance and be more resistant to atmospheric conditions?

Frank, are you observing any changes like this on your dope?

Nik

 

[Nik S]

Another question on gain twist. Would this increase barrel life?--particularly if the twist started significantly more moderate, for example starting at 11 and ending at 7?

Nik

 

[natdscott]

Not likely, particularly in light of the fact that most people who are spending $450 on a GT barrel blank are intending to push it pretty hard.

A slower twist rate might reduce chamber pressure a little at the leade, but it probably doesn't cool powder burn very much, and that plasma is what eats barrel.

If it were true that the twist rate is the problem, 14-twist .22-250s would have 10,000 barrel life, and a 7.0 twist .223 would have 1,000. They of course do not have these things.

If you worry about barrel life, keep the RPM down, clean carefully, and don't push the cartridge to the limits. Cut barrels are a good idea as well.

 

[maverickasu]

Ok... Lots of interesting stuff here... but the thing that interests me the most personally is the idea that a GT barrel would be less picky on bullets.

To the Franks and anybody who has had a GT barrel. My question is HOW not picky? Two situations come to mind for me on this...

The idea of building a 6 Creedmore and being able to take it to a match and shoot something like a Nosler 105 RDF and then take it on a predator hunt and run Hornady 87 Grain V-max at 3200+... I mean, I'm not sure it would beat out .204 for my go to varmint round... but maybe...

Second thing that comes to mind is the guy who builds the precision gun... but WONT reload... Would the "forgiving" nature of a gain twist mean that it shoots the box ammo in a more consistent way?

May be splitting hairs... but isn't that the point?

 

[Potss]

Any updates on this pressure tests at Hornady?

 

[TXSGFmrCWO3]

FYI, Rock Creek barrels are also gain twist. I learned this back in 2011 when I had my M24's in .308 and 30-06 built. Bughole.com's information page says "A little known fact about Rock Creek Barrels is that they have been using gain twist in their barrels for years. The gain is parabolic and is not a user option. It averages about .5" to .75" of twist"

The GT principle makes sense to me, regardless of whether the pressure is affected or not. I see the bullet as a fragile package of copper and lead being forced down a spiral pipe. Who knows what goes on inside the bullet? The more gradually it is spun up, the less likely damage will occur, right?

 

[sandwarrior]

As Frank Green says, the pressure does not change. The difference is that milli-micro second where the bearing surface of the bullet enters the lands. As it enters a tight twist, the front of the bearing surface is wanting to turn while the back of the bearing surface is wanting to still (not) go in that direction. If the bullet enters a much flatter twist, there will be less torsion on the bullet through the bearing surface. It then changes direction while the whole bearing surface is under control from being in the lands, and thus less torsion along the length of the bearing surface of the bullet, as the back of the bullet isn't free to not rotate yet.

So yeah, Frank Galli is right, it's the thing to do. Just not all of us have gotten there yet.

Added:
Pushing the bullet harder is only tearing it up more. There is a point at a low enough velocity it won't really show much. Then a point with these long lead filled bullets that they almost want to twist in half inside the barrel.

 

[clyancey]

About 5 months ago I too placed an order with Bartlein (6mm 8.25-7.5 twist) and was also advised to stay with an overall 3/4" twist difference. What I still don't understand is why such a small gain (3/4") when all the benefits theoretically are maximized by maximizing the gain twist.

@Lowlight you mentioned you started off conservatively but now would go more aggressive....whats the danger say with (6mm) going from 10-7.5 twist vs the conservative 8.25-7.5 twist?

Is it simply the less aggressive GT is fairly well proven and less likely to upset a customer or is there some real experience or science against maximizing gain?

 

[TXSGFmrCWO3]

As Frank Green says, the pressure does not change. The difference is that milli-micro second where the bearing surface of the bullet enters the lands. As it enters a tight twist, the front of the bearing surface is wanting to turn while the back of the bearing surface is wanting to still (not) go in that direction. If the bullet enters a much flatter twist, there will be less torsion on the bullet through the bearing surface. It then changes direction while the whole bearing surface is under control from being in the lands, and thus less torsion along the length of the bearing surface of the bullet, as the back of the bullet isn't free to not rotate yet.

So yeah, Frank Galli is right, it's the thing to do. Just not all of us have gotten there yet.

Added:
Pushing the bullet harder is only tearing it up more. There is a point at a low enough velocity it won't really show much. Then a point with these long lead filled bullets that they almost want to twist in half inside the barrel.

This all makes perfect sense to me. What would be the "perfect" twist progression? Would it make sense to start with a very low twist progressing to the desired final twist, or is that even technically feasible? Could a 6.5 Creedmoor start out at a 2:1 initially for a final 8:1?

 

[corey4]

How many shooters can actually be good enough to see the difference?

 

[natdscott]

Me.

Gain legitimately makes my rifle better at what I ask of it, which is a helluva mountain of a task.

 

[sandwarrior]

This all makes perfect sense to me. What would be the "perfect" twist progression? Would it make sense to start with a very low twist progressing to the desired final twist, or is that even technically feasible? Could a 6.5 Creedmoor start out at a 2:1 initially for a final 8:1?

This is where the science and engineering exceeds me. I understand what is going on, I don't have the mental tools or the actual tooling for that matter, to break it down to what is "the perfect" twist. I will say that twist will be for one specific bullet in all probability or a narrow range of bullet types.

For now, it's a bit of a game of elimination as to how much twist you can gain in a given barrel with a given chambering and a given bullet, or set of given bullets. What if you were aggressive and gained all you wanted, but it did no better than a less twisted barrel? For that bullet I wouldn't change, but with technology jumping right now in the LR shooting world, I wouldn't be surprised if that barrel might come in handy with a different longer bullet?

I'd hate to see the "that's good enough" syndrome set in and limit us like it has for the last 100+ years. Because, "That's the way we always twist it," means it'll take an act of congress, an earthquake and three lightning bolts to improve a twist on a given caliber 1"-2" tighter. God might even have to step in and give a nod to a new type twist before it changes.

At least this idea is moving. I'm a big fan of .257" and .277" calibers. But, damn if you can find a tight twist and a bullet to optimize that twist in those calibers. Yet, it's perfectly do-able. Mindsets have to change.

 

[TXSGFmrCWO3]

It would be wonderful if this could be a research project ranging across barrel makers and shooters. If we can see any kind of trends between the results of RH vs. LH, progressive or non-progressive twist, something more definitive might be reached.

I'm sure some engineer could devise a series of tests to determine accuracy between two different machine rest barrels.

To be honest, I would love the see a metallurgical and microscopic comparison of bullets fired.

 

[sandwarrior]

It would be wonderful if this could be a research project ranging across barrel makers and shooters. If we can see any kind of trends between the results of RH vs. LH, progressive or non-progressive twist, something more definitive might be reached.

I'm sure some engineer could devise a series of tests to determine accuracy between two different machine rest barrels.

To be honest, I would love the see a metallurgical and microscopic comparison of bullets fired.

Along the line of bullet damage, I had a .257 Wby. I bought it thinking it was a .257 Roberts. Anyhow, upon getting it, I loaded up a bunch of my favorite bullets to see what it liked. With Sierra's Bergers, and Hornady's the groups were either horrible or sometimes non-existant. With Noslers, the groups were excellent. So, I'd shoot a great group then a shitty one. I was ready to wrap that rifle around the nearest tree!! Then for whatever reason I was walking down to the 200 and as I walk up i have what looks like a little throwing star made out of copper. The bullets were coming apart! The Noslers grouped well as they have a tougher jacket.

An interesting thing about Weatherby chambers is they have a ton of freebore. This is to help the bullet get started as fast as it could. Because Weatherby started rebuilding surplus WWI rifles, he found that with crowning, they shot acceptable hunting accuracy. These were rifles that had T.E's of 5+. But, that the eroded throats could be loaded hotter and get more velocity. Anyways, he applied that principle to his rifles. As this applies to our discussion here, what if you can't run the bullet into the lands at full speed? My rifle had a 1-10" twist, so not so radical as what were talking about in this thread on the starting end. Maybe the bullet can't enter the lands at high speed and not get deformed. Maybe it was the style of lands? If the barrel were a 5R, would the regular bullets not get torn up?

This discussion really leads me to believe that to move forward gaining velocity on high twist barrels we really need to look at how the bullet enters the lands. maybe a long tapered land of low twist to start?. 5R or Metford type rifle would also be a factor in not disrupting the innards of a bullet while the lands grab hold of it. As an aside, but related, I shoot my 7mm-08 out of a 1-8" twist. I shoot 183's, 180's, 175's, 168's and 162's from that rifle and they all seem to have a 2720ish fps speed limit. I use a very slow powder to take advantage of a long barrel. But, maybe, by the bullet entering the lands slowly, it's not getting disrupted so bad. I'm not shoot hyper velocity, but I've never torn up a bullet from that rifle. Nor do I see odd fliers.

 

[natdscott]

Whatcha wanna know, sandwarrior?

Have a 5R, Lefty, CM, Gain 8-6.5", .224/.219 with what is now a 150 Freebore/1.5-degree "223" chamber.

 

[sandwarrior]

Whatcha wanna know, sandwarrior?

Have a 5R, Lefty, CM, Gain 8-6.5", .224/.219 with what is now a 150 Freebore/1.5-degree "223" chamber.

There is a world of shit I wish I knew! Half the time I'm wishing I could remember too., ha ha

So, you have a .150" free bore? Is this comp rifle like LL was talking about earlier?

Added:
I wonder how that would shoot with a matching barrel chambered in .22-250? Too much speed entering the lands?

 

[natdscott]

It STARTED as a 0.110" freebore, and is, at this point, about 0.043" eroded. Incidentally, I think I kinda like it here, and may spec the next reamer at 140 or something.

Yes, it is a dedicated 1,000 yard AR-15 Service Rifle. (Cue the poo-poos from the "Precision" crowd, but the MF shoots verticals in the ZEROES off bags, and probably MOA or a little under at the long lines.)

A .22-250 wouldn't need that much twist for the 90's unless it was really short. I only have 20" of barrel in the Tiny Tim of cartridges, and it still works at probably a 6.6" finish.

If I were doing a dedicated LR .22-250 with Gain, it would be a 28" 8.5"-to-7.0" Gain, probably in a 5R profile. I'd throat it for 80's because they are easier to tune, and frankly, I don't think the 90's will handle that kind of speed and twist....they'll come apart in the middle.

Also, in a .22, the modern 80's are going to get you almost anything the caliber can do at the kind of speeds a -250 will generate, much less a .22-243 or similar.

-Nate

 

[Lowlight]

Shot the LH GT 260 this past weekend at the Gunwerks Match, it was spectacular -

Let Phil shoot it positionally, he felt the difference

 

[MarinePMI]

Frank,

Do you know if Win Tac or any of the other AI barrel suppliers plan on offering LH GT barrels as an off the shelf item? It would seem (based on your findings) that many of us would automatically go that route if they were readily available. Just thinking out loud here....

 

[BLKWLFK9]

This may be a dumb question, but how do you properly annotate your twist rate in ballistic programs? Just 8-7 if that's what you have or is there some other way to help the program understand what you have? Im thinking about doing a LH gain for an upcoming barrel.

 

[BangBangBlatBlat]

This may be a dumb question, but how do you properly annotate your twist rate in ballistic programs? Just 8-7 if that's what you have or is there some other way to help the program understand what you have? Im thinking about doing a LH gain for an upcoming barrel.

Use the final number because that is going to be the final spin rate of the bullet.

 

[BLKWLFK9]

See... that makes sense. I would have been pissed trying to fit too many characters into the box for the twist rate, cussing at my phone.

 

[TXSGFmrCWO3]

Shot the LH GT 260 this past weekend at the Gunwerks Match, it was spectacular -

Let Phil shoot it positionally, he felt the difference

Just to refresh, what is the purpose of the LH rifling? Is it a coriolis thing? If so, would RH be better down under the equator?

 

[MarinePMI]

Spin drift going against the coriolis effect, and the tendancy for right hand shooters to pull the rifle to the right. Down under(?), then yes to the first, but not the second.

 

[sandwarrior]

I have to say, I'm not fully understanding the LH twist thing as much as I should. In one direction, say shooting north, I can see it working. Shooting in the opposite direction would it not be a disadvantage?

 

[TXSGFmrCWO3]

I think the most important consideration in the debate is the fact that issues like this are long overdue in their undertaking. Years ago, Camp Perry was the only long range game around. Now, barrel makers are being forced to consider an emerging market. Yards are like elevation. Some people are happy with flat or hilly, but more people are wanting to climb mountains.

There are many things about both internal and external ballistics that are either not understood or widely known. The LH and GT issues are only part of the equation.

 

[TripleBull]

Maybe I'm naive or maybe I don't worry too much but I think of barrels as consumables and don't stress too much about these decisions. My next build will be a 6.5 PRC that will shoot solids, so I stopped by Mile High to get advice and order a barrel. The smith talked about Frank's experience with LH GT and I gave it thumbs up. So they ordered me an 8/7 30" Bartlein and I'm just biding my time and picking up the other pieces I'll need. Just received 500 Warner 6.5 Flatlines, so I'm staring at them, looking at the calendar, thinking about dies, etc. In the time it takes to shoot it out, I'll pay attention to what I & other shooters experience and make adjustments next time around if needed. Life is good.

 

[natdscott]

Maybe I'm naive or maybe I don't worry too much but I think of barrels as consumables and don't stress too much about these decisions. My next build will be a 6.5 PRC that will shoot solids, so I stopped by Mile High to get advice and order a barrel. The smith talked about Frank's experience with LH GT and I gave it thumbs up. So they ordered me an 8/7 30" Bartlein and I'm just biding my time and picking up the other pieces I'll need. Just received 500 Warner 6.5 Flatlines, so I'm staring at them, looking at the calendar, thinking about dies, etc. In the time it takes to shoot it out, I'll pay attention to what I & other shooters experience and make adjustments next time around if needed. Life is good.

Yessir. There's a lot to be said for this approach.

I assume you went with a conventional 4 groove?

-Nate

 

[TripleBull]

Yessir. There's a lot to be said for this approach.

I assume you went with a conventional 4 groove?

-Nate

It's a 5R if I recall correctly.

 

[natdscott]

It's a 5R if I recall correctly.

Huh. Alan kinda commented that they were of the opinion the 5R may not shoot the Flatline as well as a conventional 4 groove square land.

 

[TripleBull]

Huh. Alan kinda commented that they were of the opinion the 5R may not shoot the Flatline as well as a conventional 4 groove square land.

I'll talk it over soon since it will be a while before my barrel is made. I specified Flatlines up front.

 

[natdscott]

Yeah. Not to contradict your point earlier about 'not worrying', but Dan and Alan both sorta expressed not-exactly-misgivings, but did seem to more recommend 4-groove.

The reasons why are beyond me. I just do what I'm told.

 

[Lowlight]

The simplified explanation is:

LH GT Benefits

1. Subtracting drifts vs Adding - Instead of CE and SD compounding they cancel each other out

2. Right Hand Shooter Benefits in the Northern Hemisphere, (Many rifles were LH Twist back in the day, like the Lee Enfield, they only changed after machines were designed to go right only) The recoil impulse is more in line with a Right Handed Shooter's body position. The impulse is straight.

3. The GT helps prevent bullet deformation - it's more forgiving with a variety of bullet weights, they exhibit less drift and higher BC because of less deformity

Think of it in terms of Bullet Runout in a load. A cartridge with a lot of Run out is bad, certain barrels give this effect by overspinning or deforming the bullet which increases the wobble and decreases the BC. This helps.

The negative side is they are not popular enough for it to be mainstream but I am working on that. I have yet to see a negative to running one, and I have several now.

I am sold on the idea, and this is not a new idea, just one that was hard to recreate effectively until now.

 

[TXSGFmrCWO3]

I can see why it's such an uphill battle; kind of like "why aren't we metric by now?" There's a huge investment in expensive tooling that does things "one twist and it's RH."

Outside of saving money to afford it, I guess I'll have to wait on a new barrel until I can find the right (affordable) combination of LH twist and GT in a prefit for Howa. I'm sure they're parked right next to the used unicorns.

 

[BCX]

I witnessed a GT barrel on Sunday w something like 1-14 to 1-10 in 300 WM loaded hot. After 6 shots the barrel was still cold to the touch. I couldn’t believe it!! My 6.5 PRC loaded hot w 1-7 twist is hot 10-12 inches from breech after 5-6 shots. I think my next barrel will be a GT.

 

[SingleShot85]

Bump for some thought provoking info

 

[BCX]

I spoke w Bartlein about the aggressive GT and was told its not recommended.

 

[Lowlight]

You don't need it and you really don't want it.

the Service Rifle guys are doing it, like 13-5 or 14-6 something like that, but for use, 8.25 to 7.5 is a nice number

That 3/4 Gain appears to be working out great.

I just got another that i have to shoot, a 224V Build from MHSA that is an LH GT Barrel

 

[BCX]

I think i will order a 1-8 to 1-7 on a 6.5 or 1-7.75 to 1-7.

 

[cro789]

Has anyone tried the gt in 223?

 

[MarinePMI]

You don't need it and you really don't want it.

the Service Rifle guys are doing it, like 13-5 or 14-6 something like that, but for use, 8.25 to 7.5 is a nice number

That 3/4 Gain appears to be working out great.

I just got another that i have to shoot, a 224V Build from MHSA that is an LH GT Barrel

Frank,

Are you going with a SAAMI spec'ed Valk chamber, or are you planning on throating it longer? Just curious (I have MHS doing a similar build for me, and have been thinking a lot about Padom's work on a .224V bolt action chamber).

 

[Hoyt7mm]

Altus is spinning up a 6.5 SAUM with a 1:8.5 to 1:7.7 as I type. I think I am going to move to a 1:8 to 1:7ish for my 6XC for my next barrel.

 

[Bertoli888]

@Lowlight "ELR Rifle going Left-Hand, Gaint Twist IS the right formula as you do not compound the drifts," sold. What type of the rifling's for ?

6mm
6.5mm
30 Cal