"Gain Twist" Rifling

[bergmen]

I am just reading up on this interesting rifling design (and what it is supposed to accomplish).

What I don't understand yet is how is this generated? Obviously, hammer forging won't work. Is this cut by a broaching method? The broach would need to have a unique cutter design to accommodate the variation in twist rate as it is drawn through the barrel.

Anyone know?

Dan

[divingin]

Watch a few videos on how barrels are cut rifled, and then vary the rotation rate of the barrel. It'll make sense then.

If you can imagine a multi-directional lathe (i.e. a computer controls which direction and how fast the blank turns), along with a computer controlled tool feed (controls how far into the barrel the cutter reaches), then add them together. At the breech end, the cutter moves at rate x, while while the barrel turns at some given rpm. As the cutter moves down the barrel, the rotation increases, tightening the twist rate. Repeat until you get a completely rifled barrel.

[mtenenhaus]

there's a bit of discussion on the classical process here: http://www.shilohrifle.com/forums/viewtopic.php?t=7632

i would imagine that nowadays modern methodologies are effected by computer program.

[200Apples]

I am just reading up on this interesting rifling design (and what it is supposed to accomplish).

What are you reading?

Will this newest process will aid a 175-grain spitzer in better hitting it's mark at 1000 yards? What else it is claimed to benefit? It is curious.

I would enjoy being enlightened.

[bergmen]

Excellent, thanks for these responses, very helpful!

Dan

[bergmen]

What are you reading? Will this newest process will aid a 175-grain spitzer in better hitting it's mark at 1000 yards? What else it is claimed to benefit? It is curious.

I would enjoy being enlightened.

I'm just learning of the existence of "gain twist" rifling. Some reports seem to indicate no benefit to accuracy but others do. It is just interesting from an engineering (machining) point of view.

The link in mtenenhaus post is somewhat "enlightening".

Dan

[NaClAddict]

It has to form an inverse equilateral triangle withe the node and second pressure spike to properly work. It seems like too much bullet deformity but I know nothing about it.

[200Apples]

The link in mtenenhaus post is somewhat "enlightening".

Ya, reading through that one now.

"These barrels shot like houses afire, but I've also been whipped by some fantatic shooters using what amounted to "gas pipes". These guys were past masters at doping conditions when conditions were simply horrible.
They could see changes that no one else could. They'd fire at what we thought were the worst times!"





Sometimes it's the equipment, sometimes it's the driver.

It has to form an inverse equilateral triangle withe the node and second pressure spike to properly work.

You, sir, are on another level entirely.

My compliments.

[slamfire1]

I am just reading up on this interesting rifling design (and what it is supposed to accomplish).

What I don't understand yet is how is this generated? Obviously, hammer forging won't work. Is this cut by a broaching method? The broach would need to have a unique cutter design to accommodate the variation in twist rate as it is drawn through the barrel.

Anyone know?

Dan

I read every American Rifleman and Arms and the Man article that my College Library had, back in the day when magazine collections were bound into yearly books, instead of being on microfilm. And in the 1930's there was an article about the Chattanooga Rifle Club, turkey shoots with muzzle loaders (taller than the men shooting them) and a backwoods gunsmith rifling a barrel.

The gunsmith used a cutter, and it was one cutter blade, on a machine like this one.


Those black powder barrels were wrought iron, hardly anything in a blade powder rifle needed to be steel; typically only the frizzen and spring had to be on a flintlock. Everything else could be brass or wrought iron.

With a cutting tool, and changing the spiral, you can see how they would make gain twist rifling.

You can see just how advanced modern cut rifling machinery is today, but the process is based on the same fundamentals.



I am surprised that someone is making gain twist rifling barrels for modern, smokeless calibers Bartlein Gain-Twist Barrels I am of the opinion that barrels with a taper choke, that is a barrel with a uniform twist but the internal diameter shrinks just at the muzzle, makes for a more accurate barrel, but that is only based on my experience shooting Smallbore Prone with Benchmark barrels, and a couple of 30-06 rifles which the barrel tightens near the muzzle.

I am going to claim that any accuracy claims of gain twist, are not due to the twist, but rather different lots of bullets. Bullets vary considerably in accuracy and shooters have no real ability to sort good bullets from bad bullets. You can weight bullets, you really cannot measure bullet diameters with home equipment in a meaningful way, and the most important, you cannot measure the center of gravity, bullet concentricity, and bullet dynamics during flight.

Because I have been able to go to CMP Talladega and shoot on their electronic targets, and see weird things that I never read about in popular in print magazines. And one of those things, is bullet stability at distance.

Based on my limited experience, bullets concentricity and stability are much more important to distance accuracy than the little esoteric things we can measure, such as uniform rifling twist, or gain rifling twist.

What shooters are doing, and have been doing, is more or less described by this joke:

A good Samaritan finds a drunk, late at night, desperately looking for something under the light of a street light. The drunk tells the good Samaritan that he has lost his keys and would appreciate the help finding them. After much careful looking, and walking around the circle of light given by the street light, the good Samaritan says "I can't find them, I don't think your keys are here". To which the drunk replies "that makes sense since I lost them three blocks back!". The good Samaritan then asks, "Why are you looking for them here?", to which the drunk replies "this is the only place I can see!".

And this is the predicament the shooting community has been brought to by in print media. In print media is advertising, and advertising turns the reader infantile. By emphasizing things which can be measured, and ignoring the things which cannot be measured, the shooting community is looking for answers in the wrong places, and making judgements on results, that ignore the most likely causes. All the time we read what are philosophical arguments about equipment, but no one is shooting the stuff, in controllable conditions, to prove the philosophical ideas actually work. But, it sells gear.

[theLBC]

wow, thanks for all that.

from my perspective, i thought the benefit might be slightly lower pressures as the bullet is eased into the final twist rate, but the "gain" value isn't very much so that doesn't really seem like it would be significant.

[hermosabeach]

a friend and I were bsing while driving to Front Sight... AR15- what is the ideal twist?
1:16 down to 1:7 was on the table of discussion

He said- why doesn't the industry standardize on 1:7 twist? What's wrong with an "over stabilized" bullet?

Bullet RPM = MV X 720/Twist Rate (in inches)
3,300 FPS in 1:7 twist =339,428 RPM
3,300 FPS in 1:12 twist = 198,000 RPM

There is a lot of stress on the projectile as it moves from zero spin to 330,000 RPM

There is a lot of stress on the throat of the barrel as the bullet is being spun up to 330,000 RPM and hot flames is everywhere...


I read too many years ago that a progressive twist was to spread out the duration from zero RPM to max RPM

They hoped that it would allow for thinner jackets and longer throat life...

[JackEllis]

All the time we read what are philosophical arguments about equipment, but no one is shooting the stuff, in controllable conditions, to prove the philosophical ideas actually work. But, it sells gear.

Several months back the Ultimatereloader Youtube channel had an interview with a fellow named Bryan Litz that covered some of the same ground. There are lots of things people do because that's how it's done, rather than because someone has proved that it makes a difference.

I realize some people pay a lot of attention to detail because (like my wife) that's how they are (OCD), and others pay attention to detail because it helps their state of mind when shooting matches (no nagging sense they missed something crucial). All fine, but I'm a "show me the evidence" kinda guy.

BTW, I find the targets and commentary you post pretty interesting and need to take a little more time going over them.

[bergmen]

Man, there is a lot of talent in this room! Great posts by everyone!

I'm glad I work from home or I would be busted for goofing off at my desk.

Dan

[IronsightsRifleman]

As an engineer I spend my life optimizing the hell out of every little thing. Often, my job involves finding twenty different ways of making a 1% improvement. None of the design features by themselves may be very important, but they add up. If you can achieve them at little or no cost, they are good ideas. From that perspective, it seems to me that, for a given final twist rate at the muzzle, progressive rifling would incur lower frictional forces in the barrel than uniform rifling, producing a higher muzzle velocity. That said, I would expect the difference in actual performance to be miniscule.

[LynnJr]

Slamfire1
Are those groups you posted at the various distances what you would consider to be good groups?
You mentioned F-Class friends of yours and unless I missed something all there guns should shoot considerably better shouldn't they? 10 shot groups at 600 yards should be around 5 inches shouldn't they?

As to gain twist barrels I thought the idea was to ramp up the twist to avoid torque on the rifle while also keeping the lead core of the bullet from slipping inside of the jacket?