gain twists?

[creech]

I wasn't sure where too post this, and I'm sure this has already been explained... But what the hell is the deal with gain twists? Are they just a fad or do they actually make a difference?

 

[korykhunter]

Was wondering the same thing the smith I was visiting last weekend was working on several. He explained it to me and I can see where it makes sense. By starting at a slower twist it lessens the torque on the barrel. Maybe someone else can chime in a little more. The barrels the smith was working were for a small 30 cal cartridge shooting 115s.

 

[58blackflag]

Google and ye shall find! Here is Bartlein's version...

Bartlein Barrels, Inc. - T Style Rifling

 

[SuburbanHick]

I would call bartlein.....

The way in look at it is the "normal" barrels shoot better than I usually can....so how much difference would it really make??

 

[wadebrown]

The gain twist will not reduce torque on the barrel unless the final twist is less than the rifle you are comparing it to. The torque on the barrel is strictly a function of the rate the bullet is revolving as it leaves the barrel and the time it took to traverse the barrel after leaving the cartridge. Physics is very hard to beat and you will beat your head against the wall trying to beat it.

 

[creech]

Ok I see I'm in over my head on this one. Thanks for your attempts at enlightening me fellas. I think I'll stick to more traditional rifiling.

 

[Randoman5]

Seriously. Bartlein's website said what they were capable of, not the advantages or disadvantages. What would be the purpose?

 

[korykhunter]

The gain twist will not reduce torque on the barrel unless the final twist is less than the rifle you are comparing it to. The torque on the barrel is strictly a function of the rate the bullet is revolving as it leaves the barrel and the time it took to traverse the barrel after leaving the cartridge. Physics is very hard to beat and you will beat your head against the wall trying to beat it.

Thanks for correcting me I was thinking the opposite was true. The slower twist at the chamber vs the twist at the crown but the torque is made as the bullet exits the barrel not when the bullet engages the rifling. Do I have that right??

 

[RobertB]

What it does I can't figure out either but my GAP 6.5 CM has a 20" Bartlein gain twist on it is and is an absolute hammer. But so are my non gain twist. I thought that the gain twist was a good idea for a short bbl to get the most velocity as you can. SHoots 120 and 140 grn real good. We held sub .5 moa at 1000 yds last night with it and 120 grn factory loads. Stupid accurate. Not sure how much the gain twist helps but it sure doesn't hurt.

 

[digitalshooter]

Here is what I got from Wikipedia. I don't know if it's right or not:

Rifling - Wikipedia, the free encyclopedia

Gain-twist rifling

Gain-twist rifling begins with very little change in the projectile's angular momentum during the first few inches of bullet travel after ignition during the transition from chamber to throat. This enables the bullet to remain essentially undisturbed and trued to the case mouth. After engaging the rifling the bullet is progressively subjected to accelerated angular momentum as burning powder propels it down the barrel. By only gradually increasing the spin rate, torque is spread along a much longer section of barrel, rather than only at the throat where rifling is eroded through repeated rifling engagement.

 

[SteelW0LF]

Yeah, I'm not sure where this idea that torque is applied when the bullet leaves the barrel came from, but due to the laws of physics they are claiming to quote that is impossible.

Torque is applied to the barrel when you take a non rotating bullet, and force it to start rotating with the rifling.


What the gradual progression will do is spread that torque over the small amount of time the bullet is in the barrel instead of applying it all at once. I personally don't think this could be of much benefit unless your barrel threads were such that the torque was trying to loosen the barrel. But even then your barrel would have to be so loose that the little bit of torque applied to the barrel from a small projectile could loosen it, and if it was that loose you would have other issues.

Maybe with Big bore rifles it could be a factor in accuracy if the torque being suddenly applied to the barrel could disrupt aim?? But this would automatically be adjusted for when sights are zero'd and it would be a consistent effect.... so again, I dont really see much advantage to the progressive barrels.

 

[Bruno]

I am just not really getting a clear picture of what advantages the gain twist does have over traditional. Laymans terms please...

 

[biffj]

The whole point of gain twist is to reduce chamber pressure by allowing the bullet an easier start and increasing the twist rate slowly. It takes less pressure to push it into the rifling with a slower twist.....the military has been using this in the 20mm vulcan and some of the other cannons they use like the 25mm bushmaster. I believe it allows higher velocity while keeping pressures down in the chamber. The idea of this is to increase the life of the firearm as well.


Frank

 

[Temp9]

Let me put it this way: A decrease in twist rate is extremely detrimental to accuracy. This would cause instability in the bore. While the best situation for a barrel is perfectly uniform twist rate, some people choose to avoid a decreasing twist rate by using gain rifling (increase in twist). A slowly increasing twist rate is not detrimental to accuracy, but does not offer any advantages over a properly formed uniform twist rate.

As mentioned above, a uniform twist rate is also crucial, so is matching the proper twist rate for the bullets to be used. Ideally a barrel would have a twist with no variation. If the twist rate decreases, accuracy will suffer, but a slight increase in twist is not detrimental. The explanation for this is fairly simple. If we look at a recovered bullet we'll notice that the rifling cuts a partial helix in the bearing surface of the bullet for each land. The helix is on an angle matched by the twist in the barrel. If the twist rate decreased, the angle of this helix would decrease also, and would effectively cut a wider groove into the bullet. This condition is undesirable because the bullet could then yaw while still inside the barrel. It would lack the full support of the barrel, especially on the driving side of the land. The yaw would be demonstrated by poor grouping on a target once it was released from the barrel.

Conversely, an increase in rifling pitch would tighten the angle. While this is no better than a constant twist on the bullet, it is certainly better than a decrease in twist, as we first discussed. And as we mentioned, the rate of twist must be matched to the bullet. This subject is covered in some of our other articles.

Lilja Precision Rifle Barrels - Articles: What Makes a Rifle Barrel Accurate

 

[creech]

So then basically, a gain twist simply relieves some chamber pressure which gives you longer barrel life by reducing throat erosion?

 

[jwp6114]

tag... i dont think it would greatly help an already over boar round like 243AI or 30-338LM?

 

[RyeDaddy]

I called Bartlein to ask about it when I ordered the barrel I'm waiting on. It was explained to me that the gradual increase intwist kept forward tension on the barrel, reducing harmonic distortion. As the bullet moves down the barrel it's pulling forward on the edges of the lands. Made sense to me, and for a $40 upcharge it didn't seem I had much to lose, I'm sure the barrel will outshoot me either way. I ordered a 26" barrel in 6.5 with a 8.75 tapering down to 8 twist, should be here around July.

A byproduct I've heard from others but not from Bartlein(didn't ask them), was that gain twists seem to produce higher velocities and lower pressures. Who knows if that's true.

Maybe Frank Green will log on and enlighten us. You could try PM'ing him and get it straight from the horse's mouth.

 

[longguntoter]

Some of the Italian Carcano rifles had gain twist barrels. I was reading an article about Carcanos about a month ago and was surprised to see that they did this in their standard military arms.

 

[Desert Fox]

I was wondering what is the effect of the rifling as it engage the bullet. If you start at a slow twist and progressively increase it towards the muzzle, isn't that in theory also changes the twist angle. If so what is the effect this will have on the bullet jacket.

 

[jwp6114]

I was wondering what is the effect of the rifling as it engage the bullet. If you start at a slow twist and progressively increase it towards the muzzle, isn't that in theory also changes the twist angle. If so what is the effect this will have on the bullet jacket.

this is what i was thinking, angle of groves on bullet would twist in direction of rotation...

 

[oldfatguy]

Back in the old BP days gain twist helped to keep heavy pure lead bullets from "stripping" the rifling.

OFG

 

[RyeDaddy]

I remember whoever I spoke with at Bartlein saying you don't want to go too extreme on the gain, somethijg about it having a negative effect on the bullet. Probably from what you're talking about with jacket deformation. I remember them saying about an inch of gain for 26" of barrel was about the max.

 

[Ledzep]

I'll be having fun for the next week just wrapping my head around an increasing rate of rate of twist.

I did know that they did it with cannons. I'm curious now what kind of ballistic degradation we're looking at for bullets with driving bands. A guy would think that with a driving band you could do some pretty steep changes in twist rate without worrying about damage to the jacket. Would it make a significant difference in accuracy or barrel life? can't know.

 

[nso123]

It has been used in the Rock barrels for a while. I just got my first rifle barreled by RWS with a Rock barrel, and all I can say is wow. I don't care how it works, or if it even works, but I know that the new rifle is an absolute hammer.

 

[mexicanmatch]

Go back to WWll, the German 88mm AA had a gain twist barrel and history shows how deadly they were. MM