Conventional wisdom be damned, why are long range, precision rifle shooters in the Northern Hemisphere using right hand twist barrels ?
Is employing a Gain Twist barrel a fad like some people claim, or does modern, computer controlled barrel making techniques make this old idea work better ?
For quite some time now I have been discussing these questions with the guys at Bartlein Barrels. My conversions with Trace Bartlien and Frank Green have prompted me to try this, especially being familar with their barrel making capabilities. Bartlein is using computer controlled rifling machines that take this old idea and put a modern spin on it. At Bartlein they call this, "T" style Rifling or Transitional. And before you dismiss this as a fad, realize more and more benchrest and service rifle shooters are going in this direction, so the fad is growing.
A bit of background
In the 1890s, Harry Pope was considered the finest barrel maker in the United States. He was known for his highly accurate competition rifles like the Stevens Pope Single Shot Schuetzen Rifle. He was hand making barrels that were left hand twist, as well, they were progressive, or what we are calling Gain Twists. To read more about the man, head over to the site with this quote:
"Thirty years ago, Pope records for off-hand shooting were almost as famous as Pope barrels. Once over a period of several days, he made 696 consecutive bulls-eyes at 200 yards and another time he placed fifty consecutive shots all within three and three fourths inches of dead center. His fifty-shot record, made shortly after the turn of the century, was 467. Today it is only 470. His hundred-shot record was 917. Today, the record is only 922."
Pope saw the benefits, but in researching this subject I have broken it down to the following:
1. You controlled the depth of the lands and grooves and progressively twisted the rifling so not to deform the bullet
2.The slight change in angle of rifling in connection with choke boring effectually shuts off any escape of gas and prevents gas cutting, which is another cause of imperfect delivery.
3. You had it turn left for a right handed shooter so the rifle recoiled towards the centerline of the shooter's body.
4. At longer distances, you play the Spin Drift against the Coriolis Effect instead of compounding them together.
Now many dismiss this as a fad and say progressive twists were unnecessary since jacketed bullets came into play. I honestly don't buy this and feel the difference comes down to, properly adjusting the twist to work with a jacketed bullet. As Frank Green has written, the gain twist acts like a mechanical choke which is something the benchrest crowd requests from Bartlein especially in the lapping process.
So, you have a bit of history and we all recognize this is nothing new. However nobody who talks about it mentions Bartlein and their computer controlled machines.
How Bartlein approaches the twist and the gain can be seen in the above video around the 2:00 mark.
In the Field
Okay, so not to bore you too much with the historical data, I want to talk about real life using a Gain Twist barrel. You can search "Gain Twist" in Google and there are plenty of links about the service rifles shooters and benchrest winners using the Bartlein Gain Twists, but what about the tactical shooters ?
If you go back, the GA Precision Bravo 6 Delta George Gardner made was a 6mm Creedmoor that used a gain twist. That rifle was an 8.4 at the breech and 7.7 at the muzzle. This helped push the fast and long 6mm bullets without deforming the jackets. It's not uncommon to be at a match and see a bullet come apart half way to the target. The idea of the gain twist is to keep these bullets together.
When using monolithic bullets you find bullet makers recommending gain twist barrels so to keep things like the driving bands from being torn off the bullet. My 338NM that is made for shooting a very specific 338 monolithic bullet uses a 13.5 to 5.4 twist rate. You could not put a jacketed bullet in it as it would probably come apart. But it works very well this super long 338 bullet.
We have two days and several different types of bullets downrange with the Bartlein Left Hand Gain Twist Barrel. Mile High Shooting finished my barrel to 23.5" and immediately I was out testing it using my Accuracy International AX. While the conditions were not optimal, I was still very interested in what my initial results would be.
Station Pressure: 25.30
Temperature: 25 to 35 degrees
So as you can see less than perfect.
Ammunition Tested so far:
Factory Prime Ammunition: 130gr with a recorded MV of 2760fps (SD 20.0)
Copper Creek Custom Loaded 136gr Scenar with a recorded MV of 2820fps
Andrew McCourt Handloads - 139gr Norma (43.3gr of H4350) with a recorded MV of 2760fps (SD 5.3)
We first tried each at 100 yards to see how they grouped and to record the muzzle velocity data. Next we took each of the loads out to 800 to compare the results.
Our initial group with the Prime Factory Ammo at 100 yards gave us a 10 shot group that was pretty much one hole. Understand these are all shot off a bipod, using just a rear bag and in the conditions, we had a lot things moving. Me, the target backer. The wind was pretty bad, but the initial results were outstanding.
The interesting part of this was the resutls at 800 yards. Both the Prime Ammo and the Copper Creek 136gr used the same dope to hit the 800 yard target. 5.8 Mils and the 139gr Load only need a .2 Mil adjustment to hit the same target. The zeros were pretty darn close to each other. The rifle was zeroed using the Prime 130gr bullet, the 139gr Handload was just low, about 1/4" and the 136gr Copper Creek load was just low and slightly right. But all pretty darn close to each other. Added Benefit ? Who can say ?
Our testing continues and we are taking advantage of every break in the weather. The plan is to shoot the hell out of this barrel and gather as much data as possible, recording everything I can.
My next step is to dope the rifle out as far as possible gathering data at every yard line so I can compare.
Why a Left Hand Twist, Transonic as a Buzzword
Call me crazy, I don't get the obsession with shooting beyond "Transonic". Sure I get shooting as far as possible, especially with rifles designed for it, everything from a 338 on up. But to take smaller calibers, 6mm, 6.5, and short 308s to 1 mile is a bit weird to me from a promotional standpoint. Why are we turning our high powered rifles into bad 9mms ? Sure, we shoot as far as possible because we are arrogant and we can, but to act it's viable beyond the entertainment value is a bit strange to me. Want to hit a target at 1 mile when you have a 16" 308, my advice is, getting a bigger, faster bullet. Lobbing bullets like a mortar round is a tad silly. Sure I have done it, it's a waste of ammo.
Don't get me wrong, I take shooters out to mile all the time, but I impose rules on it. It's a bucket list thing and we can certainly walk people in on target. If you can see the splash you should be able to hit the target with a few of those rounds. After all, you have to expect everything downrange to get hit at some point.
With Transonic as a buzzword, guys have taken to overspinning the bullets. Increasing the twist rate to have to better predictability at longer ranges. Doing that, why are we going to the right with everything instead of twisting left ? That is my question, and why I went left handed with this barrel. If we are slowing the bullet down so much we know we are increasing the spin drift. As well since we are shooting super far, we also have to figure in a bit of Coriolis on top of that.
Since the math doesn't lie, 2 + 2 = 4
Dr Pesja in both Modern Practical Ballistics and New Exact Small Arms Ballistics addresses this very thing in a tiny paragraph.
If were are shooting far in the Northern Hemisphere we use a left hand twist rifle, and not a right. The right hand twist is compounding every drift we have. So by going left we at least put the spin drift in our favor and counter some of the other factors. It may not make any difference inside 1000 yards, but if you're gonna shoot to 1500 and beyond, those things start to add up. It's not just shooting north, it's the entire northern hemisphere.
More math as numbers help visualize the resutls 2 - 1 = 1
It's too early to tell, and the winds were certainly too strong to notice, but it's something I am looking into.
We do it because we can, and lucky for me, I have targets every 100 yards to 1 Mile and beyond, so I should be able to see if we have a noticeable, verifiable difference.
At the end of the day, it maybe a waste of money and time but then again I think not. Frank Green is using a 1-8 Left hand twist 308, he sees something there.
We are two days into this, but honestly so far the results are promising from my standpoint, I can feel the recoil difference and believe the rifle stayed on target better. The accuracy out of 3 different loads were outstanding giving me increased flexibility. And my Accuracy International AX Platform will allow me to swap barrels with ease to compare results. I can switch from the Gain Twist barrel to a conventional 260REM barrel on the fly and note the differences under similar if not exactly the same conditions.
Thanks for reading, and standby ...