Twist

[scpaul]

Eventually I'm wanting to get a completely custom barrel. I'm going to speak in generalities because I'm not sure of the caliber yet.
I'm thinking about progressive twist, what % progression would seem reasonable.
Which type of rifling other than hexagonal?
I want to increase twist over standard for future possible higher bc projectiles but don't want to destroy projectiles due to extreme rotational force.
I know that I'm asking alot especially for such a vague caliber and projectile.
Thanks, Paul

 

[Bob Wright]

I would say it still needs to be in the same equation as chambering choice. Like 30 cal is typically 10 twist, 7mm is generally 8.5, 6.5mm is 7.5. Generally speaking and custom hand lapped barrels of course.
There are lots of factors at play. Bullet choice will be one of those.
Gain twist is rare. Not sure you need it.

 

[scpaul]

I would say it still needs to be in the same equation as chambering choice. Like 30 cal is typically 10 twist, 7mm is generally 8.5, 6.5mm is 7.5. Generally speaking and custom hand lapped barrels of course.
There are lots of factors at play. Bullet choice will be one of those.
Gain twist is rare. Not sure you need it.

I have a S&W 460. I can't remember how much but it has progressive rifling according to my paperwork. I'm thinking about starting a projectile as fast as possible without deformity or stripping the rifling and continuing it for the length of the barrel. Barrel length yet to be determined and caliber will probably have a large effect. Don't forget about the MANY variations on rifling.Configuration, even or odd grooves, ramped, clockwise or counter c.w. and the list goes on and on.

 

[Bob Wright]

Didn't know you were talking hangun. Forget everything I said. Lol.

 

[scpaul]

I wasn't talking g handgun. I was just using g it as an example of the way that you can accelerate a projectile without destroying it during the peak of the pressure spike.

 

[scpaul]

I would say it still needs to be in the same equation as chambering choice. Like 30 cal is typically 10 twist, 7mm is generally 8.5, 6.5mm is 7.5. Generally speaking and custom hand lapped barrels of course.
There are lots of factors at play. Bullet choice will be one of those.
Gain twist is rare. Not sure you need it.

I had to go in FN Mfg. at Columbia,S.C. and got some time to talk with the ballistics engineers and designers. When the conversation came around to gain twist they admitted that there was something going on but they obviously wanted to change the subject. They tried to get me oked to fire their new experimental pistol which eventually became the 5.7 round and I couldn't guess for sure which pistol. I did see some very interesting eng. drawings on some discreet walls. I also got a tour of the mfg. floor including the hammer forging barrel machine. It was lunch or i'd never have been allowed in there. There some secluded areas that we gave a wide birth. I enjoyed it bunch. I really would have loved more time with the engineers.

 

[sable tireur]

When I first started with Gain Twist barrels, the only was manufacturer was in Germany. Their ratio was fairly large. The Bartlein and a couple of others decreased that quite a bit down to 1/2" change or 1" change at the most.

GAIN TWIST

Per the Bartlein Barrels website:

I'll quote what Pope (Pope was one of the greatest barrel makers from a bygone era. His barrels along with Schalk who he learned from and gives credit to and Schoyen, and Zischang made barrels for the Schutzenfest type of guns/shooting in the late 1800's to early 1900's) said around a 100 years ago first.

"The advantages of the gain twists are three.

1st The twist being less at the breech, gives less friction to the bullet; it therefore starts easier and quicker, giving the powder less time to burn on in front of the chamber, which therefore fouls less than in a barrel of uniform twist at the same necessary muzzle pitch (twist).

2ndThe slight change in angle of the rifling, in connection with choke bore (lapping choke bore of the barrel), effectually shuts off any gas escape of gas and prevents gas cutting, which is another case of imperfect delivery.

3rd It holds a muzzle loaded bullet in position much better than a uniform twist….

Now I will add some more to this. First off I feel this applies more to a lead bullet shooter than a jacketed bullet shooter but some of the why's and why not's do overlap. With a gain twist barrel the bullet cannot go to sleep. The rifling is always putting a fresh bite on the bullet as it goes down the bore of the barrel. This is why I always go back to a cut barrel being better than a button barrel. A cut barrel even with a straight twist is more uniform and consistent than a button barrel. With button rifling the button can hit a hard spot/soft spot in the steel and it will slow the button down. The button could speed back up and do the twist it's suppose to be doing but either way you end up with a non uniform twist and it the twist keeps getting slower towards the muzzle. These two things are a accuracy killers and lead to consistency problems/fliers etc… I feel even a slight gain twist will help accuracy wise and not hurt a jacketed bullet shooter as well. For the most part I would say there is no velocity gain in a gain twist barrel with the same load. What has been conveyed to us and it goes back to Popes 1st point is that shooters have noticed that they can run a slightly heavier powder charge vs. a shooter with a straight twist barrel. As the bullet is starting easier into the rifling my only guess is the pressure isn't spiking as fast or is delaying the pressure curve. Hence forth they can get more velocity out of the gain twist barrel. I feel pressure is pressure and that the twist doesn't have anything to do with pressure for the most part but my only guess is that the gain twist like I said earlier is delaying the pressure curve. So you don't see problems as early like hard bolt lift etc… Also it's noted that even now a days our military in some 20mm and the 30mm barrels like on the A10 Warthog ground attack aircraft have gain twist type rifling in the barrels.

YouTube:

 

[std7mag]

I would say it still needs to be in the same equation as chambering choice. Like 30 cal is typically 10 twist, 7mm is generally 8.5, 6.5mm is 7.5. Generally speaking and custom hand lapped barrels of course.
There are lots of factors at play. Bullet choice will be one of those.
Gain twist is rare. Not sure you need it.

I'm thinking your an inch short on the 7mm.
Most 7s are 1:9.5.
Except Weatherby, who uses 1:10.

Factory barrels of course.

 

[scpaul]

What I'd been thinking about was starting the twist at the standard or slightly faster, depending on caliber and state of the art bullets at the time and gaining up to maybe 1 inch over the distance of a long barrel, probably 26 inches maybe a little more. Cans here are too hard and expensive so I don't expect it to be an influence. If it were to ever see the woods it be from a big stand, maybe with a recliner, it is the south after all.
Thanks for that video. The tales about Harry (?) Pope and his handloads preceeded him.
Pope and another guy built a round that was very successful. Occasional I still hear it referenced occasionally. I think it won Creedmore or another respected match 1 time.

 

[L.Sherm]

Like 30 cal is typically 10 twist,

Bob was talking 30 cal

 

[Bob Wright]

I'm thinking your an inch short on the 7mm.
Most 7s are 1:9.5.
Except Weatherby, who uses 1:10.

Factory barrels of course.

You're correct if factory offerings. I don't like those for a lot of those reasons. Reaching for a custom, it's imperative to consider bullet choices for the twist. That's why I made the comment.

 

[big7fan]

I like 8.5 and less in my 7mms.
7RM 8.4, 180 berger VLD
1st 28 Nos 8.4. 195. BERGER. EOL
2nd 28 Nos 8.0. 195. BERGER. EOL
7 RUM 8.25. 195. BERGER. EOL

 

[shinbone]

Gain twist is a pretty esoteric and complicated subject for one's first custom barrel. Kind'a like wanting to learn how to fly starting with an F-16 instead of a Cessna 150. Not to mention that gain twist has been around for a long time with hardly anyone using them, meaning, the net benefits are minimal at best. JMHO, but I'd start first by going through a few barrels of regular design from a recognized high quality maker. If those barrel prove insufficient for your application, then consider branching out into the specialized stuff. This especially without an application in mind that specifically calls for a gain twist barrel. For example, if you don't want to blow up bullets due to rotational forces, it is far cheaper and more effective to shoot a monometal bullet, rather than going to a gain twist barrel. And, I wouldn't make a move on a gain twist barrel unless and until I saw some hard data proving the design achieves what I am after.


Again, JMHO

 

[scpaul]

Gain twist is a pretty esoteric and complicated subject for one's first custom barrel. Kind'a like wanting to learn how to fly starting with an F-16 instead of a Cessna 150. Not to mention that gain twist has been around for a long time with hardly anyone using them, meaning, the net benefits are minimal at best. JMHO, but I'd start first by going through a few barrels of regular design from a recognized high quality maker. If those barrel prove insufficient for your application, then consider branching out into the specialized stuff. This especially without an application in mind that specifically calls for a gain twist barrel. For example, if you don't want to blow up bullets due to rotational forces, it is far cheaper and more effective to shoot a monometal bullet, rather than going to a gain twist barrel. And, I wouldn't make a move on a gain twist barrel unless and until I saw some hard data proving the design achieves what I am after.


Again, JMHO

Good points, I may really putting the cart before the horse. I have 1 cat that I need to finish the med/long ballistics.
I've got some stuff coming for me to change an old Rem 06 to 6mm Rem. more out of curiosity than anything else. I've never really been around small calibres much other than rimfire. I've always been the type to over do things including research and asking questions. I'll probably keep asking questions and any input will be greatly appreciated. This isn't something that I'm going to get to anytime soon. I was thinking that after I finish what I've got going maybe then and possibly upgrading the 6mm if it looks like it's worth the effort and expense. I had thought about possibly changing the 6 Rem to a 6 mm Ackley somewhere in all of this.
Thank you, Paul