What do you all think about the "Gain" or progressive rifling twist in a barrel"

[michiganmuzzy]

I'm not messing with the gain twist. It doesn't improve accuracy. I want to understand it. How can it cause the bullet to accelerate?

It doesn't CAUSE acceleration. It ALLOWS the bullet to achieve a higher velocity. the slower initial twist lets the bullet accelerate faster and then starts to twist it more quickly near the muzzle. Speed first, then add more spin for better accuracy.

 

[drpatton]

It doesn't CAUSE acceleration. It ALLOWS the bullet to achieve a higher velocity.

Bullets don't start with a high velocity, they accelerate to it. The only way to get to a higher velocity is acceleration.

 

[michiganmuzzy]

Bullets don't start with a high velocity, they accelerate to it. The only way to get to a higher velocity is acceleration.

Didnt say they start at high speed. But its not the rifling causing the acceleration. The slower rifling allows the bullet to accelerate more quickly. Where a faster twist can have the effect of slowing the rate of acceleration, the slower twist allows a faster rate of acceleration.

 

[drpatton]

Didnt say they start at high speed. But its not the rifling causing the acceleration. The slower rifling allows the bullet to accelerate more quickly. Where a faster twist can have the effect of slowing the rate of acceleration, the slower twist allows a faster rate of acceleration.

I don't know. This is something I do not understand. Given the same powder, caliber, barrel length, bullet and charge; for the bullet to exit the Gain twist faster, means the average rate of acceleration had to be faster than the non-gain twist. How? The only variable not accounted for, is the Groove Depth. Are they the same?

I can understand how a bullet accelerates to near its top velocity quicker then the acceleration slows down. This occurs with finer grains of powder. That isn't what this is.

I'm perplexed.

 

[GBG]

He claims the main advantage is not better accuracy but increased velocity over standard twist rates. As much as 300 fps.

My observations with a gain twist barrel that Bobby Hoyt did for me (.54 cal 1:70-1:48 in a 42" barrel) seems to concur with Mr. Hoyt about velocity. The original rifling in the barrel was 1:48 and I was getting 1400FPS at 15" from the muzzle (choreographed) using 70 grains of 3f and a 5.30 ball in a .015 mink oil lubed patch. With the gain twist rifling, using the same load I now get around 1675FPS and accuracy hasn't suffered.

Those are significant increases in MV. I just got very interested in gain twist. Thanks for sharing.

Does anyone know of tests/info comparing MVs of standard rifling to a smoothbore (smooth rifle) with equal caliber, length and charge?

 

[drpatton]

My observations with a gain twist barrel that Bobby Hoyt did for me (.54 cal 1:70-1:48 in a 42" barrel) seems to concur with Mr. Hoyt about velocity. The original rifling in the barrel was 1:48 and I was getting 1400FPS at 15" from the muzzle (choreographed) using 70 grains of 3f and a 5.30 ball in a .015 mink oil lubed patch.

This may be the answer. He originally had a 1:48 then he got a gain twist rifle which probibly started with a twist of 1:70 and ended up with a 1:48. I can see how that works. The same twist is achieved at the end of the barrel.

It probably takes more time and energy to force a bullet into the grooves of a 1:48 vs a 1:70. That is where the gain in acceleration occurs. The bullet slowly speeds up in rotation as it traverses the barrel.

If I am correct, given all other variables are the same, a bullet exiting a 1:70 twist barrel, will have a higher velocity than a bullet exiting a barrel with a 1:48 twist.

 

[drpatton]

The Conservation of Energy is always present, you just have figure out where it is.
In this case, it's in two places. First the energy lost to initial rotation (more loss in a faster twist).
Second, forward velocity is lost in rotational velocity down the barrel. As rotational velocity increases, forward velocity decreases. The balance of energy remains the same.

 

[drpatton]

OK. My energy is depleted and a drink will balance it out.

 

[drpatton]

Does anyone know of tests/info comparing MVs of standard rifling to a smoothbore (smooth rifle) with equal caliber, length and charge?

If my theory is correct, a patched Round Ball in a Smooth bore will be faster than a rifled barrel. Now, I say PRB, because of the need to seal the gasses in the barrel.

 

[Bad Karma]

If my theory is correct, a patched Round Ball in a Smooth bore will be faster than a rifled barrel. Now, I say PRB, because of the need to seal the gasses in the barrel.

Probably just so… also, Bobby says the recoil is reduced, in much the same way as it is in a shotgun with a lengthened forcing cone. hmmm, now Im beginning to consider gain twist in a bullet shooting rifle.

 

[michiganmuzzy]

Probably just so… also, Bobby says the recoil is reduced, in much the same way as it is in a shotgun with a lengthened forcing cone. hmmm, now Im beginning to consider gain twist in a bullet shooting rifle.

Isnt Traditions using it in some of their current guns? VAPR i think. Maybe that isnt a gain or progressive twist, tho.

 

[drpatton]

I will stick to a 1:70 twist for PRB. I have too many other things to learn and use before I try a gain twist. But now, I believe I understand the mechanics of it.

 

[drpatton]

Isnt Traditions using it in some of their current guns? VAPR i think. Maybe that isnt a gain or progressive twist, tho.

I looked up the VAPR twist and it actually doesn't say what it is, other trhan it is faster. From a 1:28 twist to a 1:24 twist. It would make sense if it were a gain twist.

https://www.traditionsfirearms.com/category/vortek-strikerfire-with-vapr-twist

 

[drpatton]

The slower rifling allows the bullet to accelerate more quickly.

I got it. That is how I believe it works.

 

[Hausser1]

The Conservation of Energy is always present, you just have figure out where it is.
In this case, it's in two places. First the energy lost to initial rotation (more loss in a faster twist).
Second, forward velocity is lost in rotational velocity down the barrel. As rotational velocity increases, forward velocity decreases. The balance of energy remains the same.

G'morn.
This is a case where a free body force diagram with a list of "Knowns" and "Assumptions", which should help identify the parasitic energy losses...
,
,
,
uh-oh. my heads hurts agin.
Why am I thinking this way? I'm retired.
Anyway, my SW460 PC Revolver has gain twist rifling.
If I do my part, it'll easily shoot the center out of a pie pan @ 200y

 

[45-70]

Probably just so… also, Bobby says the recoil is reduced, in much the same way as it is in a shotgun with a lengthened forcing cone. hmmm, now Im beginning to consider gain twist in a bullet shooting rifle.

fellow in Canada I believe makes them for BPCR

 

[user 30396]

I talked to a gun maker today and he is a true believer in the gain twist. His PRBs barrels start with a 1:70 at the breech and end up with a 1:48 at the muzzle. He uses a 42" barrel to accomplish this.

If gain twist were universally recognized as clearly superior it would be universally used.

 

[451whitworth]

I don't know. This is something I do not understand. Given the same powder, caliber, barrel length, bullet and charge; for the bullet to exit the Gain twist faster, means the average rate of acceleration had to be faster than the non-gain twist. How? The only variable not accounted for, is the Groove Depth. Are they the same?

The faster twist rate increases the pressure

 

[Charger440]

Anyway, my SW460 PC Revolver has gain twist rifling.
If I do my part, it'll easily shoot the center out of a pie pan @ 200y

I was just about to mention this..

 

[drpatton]

But its not the rifling causing the acceleration. The slower rifling allows the bullet to accelerate more quickly.

You had it figured out and I wasn't able to see it right away.