Gain twist barrels
- Thread starter PGS
- Start date
Gain twist barrels have been around since before the War Between the States. It has a resurgence from time to time as shooters and barrel makers continue to look for an "edge" in accuracy. But it doesn't seem to be there. Gain twist barrels, if they're made right, are just as accurate as constant twist barrels but apparently not more so. All that being said, I have a new gain twist Palma barrel from Bartlein sitting in the safe ready to go on the Palma rifle next year. I figured that a more gentle start into the rifling couldn't hurt at long range. We'll see 
Blair
Blair
My twin Preacher is on the right track
I used one last year but a different twist ratio in 6mm for short range.
All along i have been thinking a satandard twist was the answer,
Yes to a degree. The gain Twist is shooting far better then a straight twist so far.
I hope it works out for you also .
Good luck TWIN.
I am also trying a differnet straight twist.
I used one last year but a different twist ratio in 6mm for short range.
All along i have been thinking a satandard twist was the answer,
Yes to a degree. The gain Twist is shooting far better then a straight twist so far.
I hope it works out for you also .
Good luck TWIN.
I am also trying a differnet straight twist.
The exit twist is the twist Ie starts at 10 and leaves at 9 1/4
The final spin is 9 1/4
Now the thing the barrel maker needs to know is this''
The finish length. so when he rifle,s it progresively he knows where the exit twist is.
If you cut the barrel shorter then the exit twist specified you have a different Exit Twist.
The final spin is 9 1/4
Now the thing the barrel maker needs to know is this''
The finish length. so when he rifle,s it progresively he knows where the exit twist is.
If you cut the barrel shorter then the exit twist specified you have a different Exit Twist.
Robert and Gerry,
Just for sake of debate, if an object is accelerating in RPM at the exit of the barrel why would it not continue to accelerate for a brief moment after it exits the barrel? As I see it, it would continue at the RPM imposed by the final twist rate only if it is stabilized by a section of the barrel where the barrel twist becomes constant.
Just for sake of debate, if an object is accelerating in RPM at the exit of the barrel why would it not continue to accelerate for a brief moment after it exits the barrel? As I see it, it would continue at the RPM imposed by the final twist rate only if it is stabilized by a section of the barrel where the barrel twist becomes constant.
an interesting question.
Theory is one thing but it's differend actually.
The fastest twist is at the end of the barrel on exit. as the bullet moves through the air we get drag and the drag coefficients come into play.
actually i believe we loose spin as it looses velocity,
The object of the gain was to stabilize pressure at the breech .
This could turn into a long math equasion'
Theory is one thing but it's differend actually.
The fastest twist is at the end of the barrel on exit. as the bullet moves through the air we get drag and the drag coefficients come into play.
actually i believe we loose spin as it looses velocity,
The object of the gain was to stabilize pressure at the breech .
This could turn into a long math equasion'
Gerry,
It will definately start to decelerate in RPM shortly after it leaves the barrel. I'm talking about accelerating RPMs for maybe 10 or 15 feet after it leaves the barrel and then beginning it's deceleration in the normal manner. I don't have the equations to prove it but common sense tells me this ought to be how it works. Maybe I can entice Bryan Litz to comment!
It will definately start to decelerate in RPM shortly after it leaves the barrel. I'm talking about accelerating RPMs for maybe 10 or 15 feet after it leaves the barrel and then beginning it's deceleration in the normal manner. I don't have the equations to prove it but common sense tells me this ought to be how it works. Maybe I can entice Bryan Litz to comment!
As I was told by my barrel make the gain is increased only slightly during the rifling process . The gradual effect . that's why you have to specify what the barrel length finished will be.
Your right as to the decellarion and spin from a common sense point.
The rules of physics are a constant.
Im finding that the spin versis bullet weight are another subject too.
The formula is basic and not conclusive as to twist rate .
I see some things going on and am experimenting with one bullet weight and changing twist rates slightly to find the maximum accuracy with one particular bullet, weight shape
I'm concerned only with the short range right now. 100 200 300
Your right as to the decellarion and spin from a common sense point.
The rules of physics are a constant.
Im finding that the spin versis bullet weight are another subject too.
The formula is basic and not conclusive as to twist rate .
I see some things going on and am experimenting with one bullet weight and changing twist rates slightly to find the maximum accuracy with one particular bullet, weight shape
I'm concerned only with the short range right now. 100 200 300
Bryan Litz Ballistics
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You might regret that
As soon as the bullet emerges from the barrel, it's spin rate begins to slow down. This is true for constant twist barrels and gain twist barrels.
An objects acceleration (linear or rotational) is proportional to the forces applied. When the bullet is released from the barrel, it's in free flight, and the only forces are aerodynamics and gravity. Neither of these forces will cause the bullet to spin faster than it was when it came out of the muzzle.
A bullet can continue to accelerate (linearly) for an inch or two because of the muzzle pressure (blast). But there's nothing that will continue to accelerate the spin rate.
Gerry,
How can you attribute small differences in precision to small differences in twist rate? When you change the twist rate, you're changing the whole barrel including the action threads, chamber, throat, leade, crown, etc. If you're just chopping off a gain twist barrel to achieve different spin rates, you're still talking about differences in barrel length/harmonics. In other words, you can't just change twist without changing other variables that affect precision, so you can't directly observe the effects of spin rate on precision.
Stability is a gray area that depends on velocity and atmospherics for a given bullet. Even if you are able to identify a specific stability factor which results in best precision for one situation, that stability factor will be different from that same barrel when the air temperature changes.
-Bryan
Not lasting to long? I kinda agree but the one thing I would add is that anyone that did do it either couldn't do it in quantity and or on a regular basis or couldn't offer the variety of options that someone would want with either calibers or twist etc... They might not have seen a demand for it so didn't make them anymore also and just stopped offering them.
It started with us by guys saying can you do it? The answer was yes and it started with the cast lead bullet shooters shooting the Schutzen fest type rifles (Win. HI Walls, Marlin Ballarrds etc....) that's how we got into it.
Then Boyer asked us about making a couple and gave us the spec. on a barrel that he had several years ago that shot really well but no other barrel maker could replicate it. Sounds like it happened by accident more or less. We did he shot very well with it and now people are taking a look at it again.
Also the reason we wanted to do gain twist barrels is for ammunition test barrels. The 20mm that our military uses for the most part are all gain twist.
Later, Frank
Bartlein Barrels
It started with us by guys saying can you do it? The answer was yes and it started with the cast lead bullet shooters shooting the Schutzen fest type rifles (Win. HI Walls, Marlin Ballarrds etc....) that's how we got into it.
Then Boyer asked us about making a couple and gave us the spec. on a barrel that he had several years ago that shot really well but no other barrel maker could replicate it. Sounds like it happened by accident more or less. We did he shot very well with it and now people are taking a look at it again.
Also the reason we wanted to do gain twist barrels is for ammunition test barrels. The 20mm that our military uses for the most part are all gain twist.
Later, Frank
Bartlein Barrels
Jerry,
Yep, I noticed that. But now I think people are being a little more sensible about it. Like Frank said, the lead bullet folks are fond of it and have been since the 1870's. But whereas the folks at Harpers Ferry were using huge increases in twist rate in musket barrels in the mid 1800's, people are now using very small increases in twist rate such as 1 inch and even 1/2 inch. As for acceleration after the bullet leaves the barrel, I sure can't prove anything so I have to accept what others believe they can prove. I can take it either way. It seems that once a body starts in motion it tends to stay in motion until other forces begin to act on it and force it in another direction. In other words, once acceleration is applied to a bullet to rotate it, it would continue to accelerate briefly after exit because the bullet has still has momentum forcing it in that direction. Opposite forces start acting on it immediately after exit and the RPM begins to slow. A gain twist applies RPM acceleration to a bullet but a constant twist does not. Therein lie my suppositions
Yep, I noticed that. But now I think people are being a little more sensible about it. Like Frank said, the lead bullet folks are fond of it and have been since the 1870's. But whereas the folks at Harpers Ferry were using huge increases in twist rate in musket barrels in the mid 1800's, people are now using very small increases in twist rate such as 1 inch and even 1/2 inch. As for acceleration after the bullet leaves the barrel, I sure can't prove anything so I have to accept what others believe they can prove. I can take it either way. It seems that once a body starts in motion it tends to stay in motion until other forces begin to act on it and force it in another direction. In other words, once acceleration is applied to a bullet to rotate it, it would continue to accelerate briefly after exit because the bullet has still has momentum forcing it in that direction. Opposite forces start acting on it immediately after exit and the RPM begins to slow. A gain twist applies RPM acceleration to a bullet but a constant twist does not. Therein lie my suppositions
Ok ' lets look at actual results as far as testing has done by me so far.
I started with the standard 14 twist rate. Groups were good and about average for people using a 14 twist.
The i went to a 13 1/2 and the groups improved quite a bit.
Now i am going with a 13 1/4 to find out if there will be any improvement.
Mind you i am using 1 bullet and 1 bullet weight that i make myself.
Cases are the same weight primers the same and charge weight are adjusted as to the particular day.
I tried the gain twist from about 14 and exiting at 13 1/4 given length 22 inches.
I have 2 barrels on order for testing. i'll know ,more as time goes on.
My next twist will be the 13 and a slightly different weight bullet and also the same bullet. And bullet shape
A lot of theory is just that theory. Let see what happens in the real world.
I could do a ton of math and a gaggle of formuli to prove a point but to the average shooter it would be just too confusing to calculate.
That said the proof is in the Testing. spin and rotational axis do change even with a slight gain in twist rate
Spin and rotational axis
I started with the standard 14 twist rate. Groups were good and about average for people using a 14 twist.
The i went to a 13 1/2 and the groups improved quite a bit.
Now i am going with a 13 1/4 to find out if there will be any improvement.
Mind you i am using 1 bullet and 1 bullet weight that i make myself.
Cases are the same weight primers the same and charge weight are adjusted as to the particular day.
I tried the gain twist from about 14 and exiting at 13 1/4 given length 22 inches.
I have 2 barrels on order for testing. i'll know ,more as time goes on.
My next twist will be the 13 and a slightly different weight bullet and also the same bullet. And bullet shape
A lot of theory is just that theory. Let see what happens in the real world.
I could do a ton of math and a gaggle of formuli to prove a point but to the average shooter it would be just too confusing to calculate.
That said the proof is in the Testing. spin and rotational axis do change even with a slight gain in twist rate
Spin and rotational axis
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