Gunsmithing Question about gain twist rifling.

[Eagle1899]

Alright, I need barrel makers, gunsmiths, smart fellers and tire kickers like me in on this.

Would a barrel that started out with NO twist and progressed to a normal twist over its length work? Say 1-1 to 1-8 over 28-30 inches. Instead of the bullet starting to turn prior to being fully engaged to the rifling, straight twist would allow the bullet to be fully in the rifling (dependent on length of the bearing surface) prior to it beginning to spin.

Is this even possible? Or has it already been tried and discarded?

Would this lower pressure (friction) at the throat?

Just thinking out loud here.

 

[Turd in the Pool]

Forget it. There has been much experimenting in this avenue and no one has perfected it, some day technology my catch up. As for now, just be glad that bbl makers have achieved what they have.

 

[Graham]

I don't think you will be able to successfully reinvent the wheel.

 

[wilecoyote]

solution adopted on some italian '91 Mannlicher-Carcano, if I don't go wrong_
(...that's enough to discard it, in my book)

 

[biner626]

A 1:1 is one twist in 1". 1:600 is still going to twist. Your thought process is interesting though. But, we are talking about superheated gasses affecting a small surface area. If you blow through a small straw vs a large straw which moves air at a higher velocity? This is one of the reasons .243's burn barrels faster than a .308's. Personally, I would just go with what the barrel manufacturer suggests.

 

[Graham]

Don't all rifles start with a throat that is effectively at a zero twist rate?

 

[Turd in the Pool]

Don't all rifles start with a throat that is effectively at a zero twist rate?

Perspective is everything. Zero twist only affects the bullet before it hits the lands. After that, it is a matter of what the components do with the energy.

 

[Graham]

Perspective is everything. Zero twist only affects the bullet before it hits the lands. After that, it is a matter of what the components do with the energy.

Hopefully they keep the pressure curve on the driving side of the lands.

 

[Turd in the Pool]

Yes Sir. Sucks to have a locked action. Kind of fun to play with things but physics are pretty well established.

 

[Turd in the Pool]

Ken Waters' approach with duplex or triplex loads makes more sense to me than the gain twist angle. PITA but he gets there.

 

[Scuzy]

I like the idea of increasing the twist from near zero up to something useful in the length of the barrel.
My concern with this is that the lead of the thread will not be content, so the jacket of the bullet will be constantly re engraved and deformed. If the twist varies too much, I can see the bullet being de-jacketed. Think of trying to thread a screw in to a nut of a slightly different pitch, it will bind or strip.

I wold expect load development for this barrel would be interesting. Ill bet it would see higher pressures and may get by with less powder.

 

[Turd in the Pool]

I like the idea of increasing the twist from near zero up to something useful in the length of the barrel.
My concern with this is that the lead of the thread will not be content, so the jacket of the bullet will be constantly re engraved and deformed. If the twist varies too much, I can see the bullet being de-jacketed. Think of trying to thread a screw in to a nut of a slightly different pitch, it will bind or strip.

I wold expect load development for this barrel would be interesting. Ill bet it would see higher pressures and may get by with less powder.

Wish I could understand what you're saying. Seems to defy everything I know.

 

[xdeano]

I like the idea of increasing the twist from near zero up to something useful in the length of the barrel.
My concern with this is that the lead of the thread will not be content, so the jacket of the bullet will be constantly re engraved and deformed. If the twist varies too much, I can see the bullet being de-jacketed. Think of trying to thread a screw in to a nut of a slightly different pitch, it will bind or strip.

I wold expect load development for this barrel would be interesting. Ill bet it would see higher pressures and may get by with less powder.

I couldn't agree more. It would really mess with the engraving on the bullets bearing surface. Going from --- to \\\ just doesn't work with zero to 8T. I'm no barrel maker but physics don't lie.

xdeano

 

[Turd in the Pool]

I couldn't agree more. It would really mess with the engraving on the bullets bearing surface. Going from --- to \\\ just doesn't work with zero to 8T. I'm no barrel maker but physics don't lie.

xdeano

This shit happens with every shot regardless of twist.

While you are educating us on physics, Please explain to me and a shotgun slug in a smoothbore about pressure and powder charges.

 

[Sigma05]

The way I see it is that there already is the manufacturing possibilities to make barrel/rifles that shoot incredibly accurately. Why drive yourself crazy?


"Ex Umbris Venimus"

 

[Lowlight]

Bartlein can do it, the question is will they and will the bullets hold up.

They are computer controlled and have been quietly doing Gain Twist Barrels for different reasons.

Most of the gain twist stuff nowadays is very subtle and not as aggressive.

For testing some 338 Monolithic bullets they did a pretty crazy gain twist that I have, also I believe George competed in an F Class using a subtle 308 Gain Twist, etc.

Time and money is all, how long do you mind waiting and how much do you want to pay.

But they are pretty much the most advanced barrel maker, if they can't do it, nobody can. Also will they recommend your twist requirements ?

 

[Eagle1899]

OK, this is good! Lots of ideas, speculation and hands on experience. I started this thread to see what information is out there.

Bullet deformation due to twist change is interesting. With copper and lead being very malleable, where is the limit? How much change can a bullet take before accuracy suffers or the bullet fails.

I have no intention of having a 0-8 twist barrel built. Good barrel building practices are well established. But, thats no reason to keep trying different things.

 

[Graham]

Bartlein can do it, the question is will they and will the bullets hold up.

They are computer controlled and have been quietly doing Gain Twist Barrels for different reasons.

Most of the gain twist stuff nowadays is very subtle and not as aggressive.

For testing some 338 Monolithic bullets they did a pretty crazy gain twist that I have, also I believe George competed in an F Class using a subtle 308 Gain Twist, etc.

Time and money is all, how long do you mind waiting and how much do you want to pay.

But they are pretty much the most advanced barrel maker, if they can't do it, nobody can. Also will they recommend your twist requirements ?

I have a 7mm that starts at 9.5 and ends at 8.9. That's just enough to drive the bullets a bit differently than a standard barrel. That said, the bullets don't know how fast they are spinning and the rate at which they leave the muzzle is the operative number anyway. The barrel shot very well as a .284 with 180 VLDs, but for some reason only lasted 1800 rounds. I am now having it set back.

I would also like to try a 6.5 that starts at 9 and ends at 8.

 

[turbo54]

Just a thought:

It is pretty easy to tell the difference between bullets fired from a revolver vs a semiauto, because revolver bullets are going much faster when they engrave the rifling. That literally creates skid marks on the bullet, because the bullet "slips" in the rifling a little at first.

Revolvers shoot pretty nice...

 

[Eagle1899]

I have seen the "skid marks" on revolver bullets. No twist at and just past the forcing cone of a revolver may be worth exploring. It may allow for the bullet to enter the bore before it starts rotational acceleration.

To what end....? Like you said, revolvers can shoot pretty nice.

 

[Eagle1899]

Keep the ideas coming. This is good.

 

[Eagle1899]

Frank, Would it be possible for you to share what twist barrels were used in the Monolithic test? Results?

 

[Turd in the Pool]

Rob Turner from this area has had Pac-Nor make gain twists for years. Nothing spectacular comes from it. Multiplex powder charges do more for velocity than gain twist. I never could understand why anyone would want to deform a projectile more than necessary.

 

[Eagle1899]

Velocity is great, but not the focus of my interest in gain twist barrels. Mixing powder (other than same powder, different lot#) is way on the outside of what I'm curious about.

Barrel life, accuracy, bullet performance (as it relates to the barrel, not terminal performance) are the goal.

 

[Graham]

Rob Turner from this area has had Pac-Nor make gain twists for years. Nothing spectacular comes from it. Multiplex powder charges do more for velocity than gain twist. I never could understand why anyone would want to deform a projectile more than necessary.

Gain twist is not employed for the purpose of producing increased velocity.

 

[my human host]

While it's not a gain twist scenario, some of you might find the Holland Paradox interesting. Kinda takes freebore to the extreme.

 

[Rthur]

There were some articles written by David Tubb(I believe). He shot many barrels and noticed that some were noticeably more accurate from the beginning of their use. After some inspection they all seemed to have a slight increase in barrel twist. As far as the reason Bartlein and others are doing it, George might be the guy to answer this.

R

 

[Turd in the Pool]

Gain twist is not employed for the purpose of producing increased velocity.

Please enlighten me. Why else would you do it?

 

[turbo54]

Please enlighten me. Why else would you do it?

Real or perceived accuracy advantage.

Truth be told, I don't see the point. Benchresters have been printing tiny little groups a long, long time. Sure, advancements are made, and oughtta be used as applicable.

We all know a 3, 4, 5 or 6 groove or 5r, cut rifled, hammer forged or button barrel chambered properly can and will be reliably shoot sub 1/2 moa. Clearly that's not adequate for bench rest, but its plenty good for the "serious tactical marksman".

I've yet to see a tactical match won by someone that *wouldn't* have won with a 3/4 moa rifle.

I'm an engineer, and appreciate science and technology, but the activities we come to this website to talk about simply don't need that extra .025" at 100 yards.

 

[Eagle1899]

You may not "need" that little extra but why leave it on the table....... Confidence in our rifle, scope and gear makes doing our best that much easier.

Would you go to a shoot with a rifle that would only do 1/2 MOA groups and no better? How about a scope that tracks mostly OK?

"Only accurate rifles are interesting" The rest get sold...

But we are getting off track. This is not about what we need, it's about what's possible.

 

[turbo54]

Would you go to a shoot with a rifle that would only do 1/2 MOA groups and no better?

Abso-fucking-lutely... and if I lost the match, *I* lost the match, not the rifle.

How about a scope that tracks mostly OK?

That's not analogous.

This is not about what we need, it's about what's possible.

4 groove conventionally rifled barrels win bench rest matches all the time.

 

[turbo54]

At some point, we have to recognize that external factors like propellant variations, bullet variations, wind, etc etc have more affect than the manner in which the tube had grooves scraped into it.

 

[Eagle1899]

You are missing the point. I asked about gain twist barrels and what's possible.

If your happy with 1/2 MOA from a custom rifle then please continue to use them.

 

[Eagle1899]

Tony Boyer shoots gain twist cut rifled barrels on occasion , just saying.......

 

[turbo54]

You are missing the point. I asked about gain twist barrels and what's possible.

If your happy with 1/2 MOA from a custom rifle then please continue to use them.

No, I believe you are missing the point.

Conventionally rifled barrels already approach perfection. If you can shoot a .050" group, do you think changing the style of rifling is going to get you a 0.00 group?

I contend barrels are already not the proverbial "weakest link".

 

[J E CUSTOM]

I am no expert by any means but I have done extensive research in to Gain Twist , and there uses.

Starting with no twist and going to a fast twist just doesn't work because the engraving of the bullet has to much change from zero to a fast twist to
be accurate.

It is normally only one or two inches of change and is used for extremely fast bullet velocity. The Gain Twist makes starting the bullet rotation
easier on the bullets jacket and prevents separating it from the bullet core.

I was considering a Gain twist barrel for a high velocity project (4500 ft/sec+) but decided on a slower twist 1 in 15 for ease of engraving and bullet
integrity. And at the velocity reached so far (4555 ft/sec) with no problems and potentially 46 to 4700 ft/sec it appears to be the best choice.

In theory the gain twist makes sense and should start the bullet a little slower and then speed it up to a good stabilizing twist rate. But so far
I have not read of much success with it.

This is just my opinion based on my studies. I would have to say there would be no advantage over conventional rifling.

J E CUSTOM

 

[oldfatguy]

Gain twist is a very old idea. It was used to keep very heavy lead bullets from "stripping the rifling" in muzzle loaders.

OFG

 

[Turd in the Pool]

Real or perceived accuracy advantage.

I get the idea. Kind of like a top spinning faster as the string runs out. If it can be proven that the projectile rpm continues to increase after it leaves the muzzle I'd be interested. I'm not an engineer and I don't buy much theory.

Barrel makers have a hard enough time making them perfect with a fixed twist. Guess it just takes a little more lapping compound for a gain twist.

 

[Eagle1899]

No, I believe you are missing the point.

Conventionally rifled barrels already approach perfection. If you can shoot a .050" group, do you think changing the style of rifling is going to get you a 0.00 group?

I contend barrels are already not the proverbial "weakest link".

I don't know what changing the rifling can and will do. That is why I asked. I did not ask about group size, velocity or life of the barrel, powder, bullets or what you are content with.

I'll say it one more time.... I want to know whats possible with gain twist barrels. Thats all.

If higher velocity is possible?, thats what I want to know. Will the throat last longer? Does it affect circular dispersion? Are they more sensative to bullets with short or long bearing surfaces?

Does chamber pressure vary based on the rate of gain? Does velocity (pressure) vary based on number of lands vs gain in twist?

As an engineer I would think you be intersted in the varible instead of the constant. But It appears that I'm wrong.......

 

[Red_SC]

I get the idea. Kind of like a top spinning faster as the string runs out. If it can be proven that the projectile rpm continues to increase after it leaves the muzzle I'd be interested. I'm not an engineer and I don't buy much theory.

I think the point isn't that the rpm increases after it leaves the muzzle. Instead, it's that the RPM of the bullet is constantly being driven higher inside the barrel, so the leading edge of the land is always in firm contact with the groove in the bullet in order to spin it faster. As you know, twist rate isn't perfect inside a barrel, and some barrels that are rifled conventionally actually slow down slightly towards the muzzle. As a result, the bullet can switch from being pushed by the leading edge of the land to riding the back side of the land. It's a slight difference, but some people's testing has pointed to this instability creating a slightly less accurate barrel.

 

[Turd in the Pool]

As you know, twist rate isn't perfect inside a barrel, and some barrels that are rifled conventionally actually slow down slightly towards the muzzle. As a result, the bullet can switch from being pushed by the leading edge of the land to riding the back side of the land.

That could be but as far as I know, most blanks are rifled before they are contoured. Unless the dumbass doing the contour accidentally sets it up "backwards", the slow end should be the chamber. I also doubt cut rifled bbls vary much in twist after lapping unless it is intentional. Depth of cut is another thing.