Gain Twist Barrels?
- Thread starter danny
- Start date
i had to try one in a 40 cal long range black powder cartridge rifle.
the intent was to shoot bullets with the same b.c. as 45 cal rifles with less recoil, so it needed a faster than usual twist to shoot longer than usual bullets.
it goes from 1/26 to 1/13 over a distance of 30".
one of its big strengths is that it shoots bore diameter paper patched bullets, possibly because it causes the paper to strip better than conventional non gain twist.
in fact it has a pp load that is the standard to judge grease groove bullet accuracy by, and none have equalled the pp load to date.
this rifle has only been shot out to 1000 yds so far, but delivers from 200 to 1000 consistently.
what is interesting about these rifles is that they are transonic from the muzzle to 600 or 700 yds.
modern smokeless guys avoid this like a dose of ebola, but designed and loaded properly, bullets can travel through it with good accuracy.
keep safe,
bruce.
the intent was to shoot bullets with the same b.c. as 45 cal rifles with less recoil, so it needed a faster than usual twist to shoot longer than usual bullets.
it goes from 1/26 to 1/13 over a distance of 30".
one of its big strengths is that it shoots bore diameter paper patched bullets, possibly because it causes the paper to strip better than conventional non gain twist.
in fact it has a pp load that is the standard to judge grease groove bullet accuracy by, and none have equalled the pp load to date.
this rifle has only been shot out to 1000 yds so far, but delivers from 200 to 1000 consistently.
what is interesting about these rifles is that they are transonic from the muzzle to 600 or 700 yds.
modern smokeless guys avoid this like a dose of ebola, but designed and loaded properly, bullets can travel through it with good accuracy.
keep safe,
bruce.
I seem to be in the dilemma of the century, for me....? What to choose, what is optimum for my build..? I am no expert on the mater thus my being here on the forum. Part of me wants a bit of gain in my next barrel. I know people are shooting great with & without. Now I'm just trying to pick the rate of gain for me...? Originally I was thinking of something like a .500 or .750 gain on a 30 inch barrel for the 90 gr vlds. But now I've learned that only a slight .100" or .250" gain has shown to really work good and most of the top shooters in the game are using those rates of twists or something close to them. Right when I was ready to go for the .750 rate of gain I learned this..! These 90s will be pushed out of a 220 Swift Improved so I can get them moving no problem 3400 to 3600. Now I'm procrastinating between .250" of gain or .750"...? Before I learned about this slight bit of gain working well I was pretty much set on doing something like a 7.500 t0 6.750.........now I'm kind of undecided again. I can develop loads for what works but really don't have tons of time to tinker around with various barrels & gain twist rates. There is a lot of knowledge here that I am hoping will save me some grief getting my choice narrowed down started in the right direction. Here where I am at in Montana my typical shooting I would say is 2900 feet @ 70 degrees, which gives me comfortable stability/1.76 with a 6.8 twist. I am not in a rush on the barrel I probably in all actuality won't pull the trigger on it until this Fall or the following Spring. my stand by gun is still doing it's job just fine with 55 gr ballistic tips! Thanks for any help
The one issue mentioned is the need to change the grooves on the bullet as it moves through the barrel. Example: say a barrel has initial twist rate at 1 to 24", the initial engraving of the rifling will have only a slight angle. say the final rate of twist is 1 to 10" and that the shift from 24 to 10 was at a constant rate. Upon firing the bullet would encounter the rifling and be engraved by the initial angle determined by the 24" twist, but as the bullet was pushed through the barrel, metal on the bullet would need to be reshaped to the final angle determined by the 10" twist. This increasing rate of twist is also occurring at the same time the rate of spin is increasing due to the bullet gaining velocity as it moves through the barrel. I have no direct experience with gain twist barrels, other than the academic investigation of the topic by reading reviews of the various military rifles that utilized gain twist and didn't appear to yield any significant benefits.
After having played with them many years ago , my opinion is that the benefits of a gain twist are somewhat caliber specific..
Our first ventures were using a 1:9-1:8" twist in 6.5 hoyer as well as 1:12-1:10" in 30X378 Wthby.
The general consensus at the time was with the given components we had at our disposal such as H5010 , H870 along with seirra MK's we were hoping to cheat if you will pressure spikes in the name of higher velocities.
After having created more than a few tomato stakes from testing we concluded that for those calibers with those components , the juice wasn't worth the squeeze.
Times have changed along with components. I would like to revisit the gain twist in a 6.5x47 imp with a 30" length and a .190" fb using a 1:9-1:8" and VV N-550 , comparing the results with other db powders such as RL-17 etc .
If your smith has a thing for gain twists, ask him the hard questions... Why and why for my project?
Good luck
Our first ventures were using a 1:9-1:8" twist in 6.5 hoyer as well as 1:12-1:10" in 30X378 Wthby.
The general consensus at the time was with the given components we had at our disposal such as H5010 , H870 along with seirra MK's we were hoping to cheat if you will pressure spikes in the name of higher velocities.
After having created more than a few tomato stakes from testing we concluded that for those calibers with those components , the juice wasn't worth the squeeze.
Times have changed along with components. I would like to revisit the gain twist in a 6.5x47 imp with a 30" length and a .190" fb using a 1:9-1:8" and VV N-550 , comparing the results with other db powders such as RL-17 etc .
If your smith has a thing for gain twists, ask him the hard questions... Why and why for my project?
Good luck
I can see it being an advantage for soft cast bullets, where there is a problem with stripping and the bullet material is plastic enough to adjust easily. When you look at the actual angles involved, it's a pretty small change, so it probably won't shear much. Given that a .224 bore with 1:14 twist has a pitch of 2.878°, tightening up to 1:10 would change that pitch to 4.025°. So you have an engraved ridge on the bullet rotating by a little over 1.1° in whatever barrel length is involved. Assuming a bearing surface of 1 inch just for convenience (awfully long for a .224 out of 1:10), and assuming the ridge rotates around the center, each end of the ridge moves by 0.0096 inch. Bullet jacket material is not particularly brittle, so there's probably not an issue there.
Yes, gain twist barrels are accurate. I'm not convinced that it is due to the gain, rather look at the barrels. You don't see any Marlin Microgroove gain twist barrels, and you probably won't see one installed on a Mauser 96. They are expensive barrels from the best makers. Since the majority of barrels are NOT gain twist, the ones that are get special attention. I think any barrel that got individually fussed over by a top line barrel maker, installed on a rifle that someone is putting a lot of time and money in, would be amazingly accurate. Add to that the Magic Feather effect of a shooter that really believes he has found an edge, and you have a heck of a shooter.
Yes, gain twist barrels are accurate. I'm not convinced that it is due to the gain, rather look at the barrels. You don't see any Marlin Microgroove gain twist barrels, and you probably won't see one installed on a Mauser 96. They are expensive barrels from the best makers. Since the majority of barrels are NOT gain twist, the ones that are get special attention. I think any barrel that got individually fussed over by a top line barrel maker, installed on a rifle that someone is putting a lot of time and money in, would be amazingly accurate. Add to that the Magic Feather effect of a shooter that really believes he has found an edge, and you have a heck of a shooter.
It seems to me that the main problem with gain-twist barrels is the change in the angle of engraving on the bullet. so what would happen if a different type of rifling was used? The types of rifling where there are no sharp edges engraving the bullet, such as the oblong where the bore is narrower for the "lands portion" then tapers out to "groove" dimensions. So the rate of twist could increase with no adjustment being made to the surface of the bullet?
I'm no expert, but I don't believe keeping bullets from blowing up is a benefit, or purpose of a gain twist barrel over constant twist rifling.
I see the benefits to being:
less initial torque, and less initial internal pressure(for a given load), as these develop more moderately as the bullet accelerates down the barrel, both in velocity and rpm.
The end result: bullet velocity, and rpm at the muzzle should be similar for both constant pitch, and gain twist rifling.
Over 60 years of shooting I've shot quite a few barrels; from custom to factory and they all worked pretty good! Here's ten shots fired recently from 900 yards with just a standard Remington factory barrel. I've had very few customs that would do the same! Whatever blows ya skirt up!
308 Win/Remington M700 factory barrel/action by Sharps Man, on Flickr
308 Win/Remington M700 factory barrel/action by Sharps Man, on Flickrdcali
Bullet Maker
How about this for a theory on why gain twist *might* help accuracy:
My understanding of the concept is that it is used in larger bore heavy weapons because the torque required to spin up a large projectile can be enough to stress the bearing surface enough to shear the surface. With small arms, that's not an issue. Bullets can withstand the shear stress without coming apart and still maintain acceptable performance.
But... when talking about hyper-accurate benchrest-grade precision, the outer surface of the bullet is important - just look at the tolerances on a BR grade bullet jacket. Maybe the reduced stress (because of the lower torque on the bullet) helps precent inconsistent rifling grooves, thereby promoting better balance, and letting a high grade bullet keep just a hair more of its inherent precision.
Just a half-baked thought.
My understanding of the concept is that it is used in larger bore heavy weapons because the torque required to spin up a large projectile can be enough to stress the bearing surface enough to shear the surface. With small arms, that's not an issue. Bullets can withstand the shear stress without coming apart and still maintain acceptable performance.
But... when talking about hyper-accurate benchrest-grade precision, the outer surface of the bullet is important - just look at the tolerances on a BR grade bullet jacket. Maybe the reduced stress (because of the lower torque on the bullet) helps precent inconsistent rifling grooves, thereby promoting better balance, and letting a high grade bullet keep just a hair more of its inherent precision.
Just a half-baked thought.
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