Home Forums Hunting & Shooting Ask The Gunwriters gain twist barrels

Mine are plenty accurate.Ain't talking about what it shoots into a inch.My first posts states they can be tricky to load for.I'm talking speed man speed.

You're burning more powder to get to the same peak pressure.

The angular momentum of a bullet carries about 1/2% of the total energy of the bullet.

Has anyone ever made measurements to support the notion that gain twist rifling actually produces more area under the curve? So little of the bullet's energy is in angular momentum, that I have difficulty imagining how such a minor change in how that angular momentum is acquired would make any large difference in total energy.

How do we know that the difference is not simply from tighter chambers and higher peak pressures?

Did not Roy Weatherby go with a long freebore to reduce inital peak pressure when the bullet hits the rifling?

Just curious, because the explantion that a gain twist reduces pressure peak pressure at the same point (inital contact with the rifling) seems to reasonable.

If I were manufacturing a lot of rifles (like Roy did) I would probably choose the (presumably) easier manufacturing method -- the freebore.

Just thinking out loud.

BMT

Therein lies the crux of the issue. I have never experimented with a gain twist barrel, nor do I know of anyone who has invested the time and money into pressure testing barrels of any known quantity.

As an aside...isn't there some friction reduction too? The bullet is spinning less in total as it traverses the length of the bore in the gain twist barrel. How much energy savings from this? Combined with the energy saved from imparting initial angular momentum, would it be enough to make a 100 FPS difference in velocity?

Say you have a 100 gr bullet at 3000 FPS...thats 1963 ft-lbs. Add 100 FPS and you have 2096 ft-lbs. A 6.7% difference in energy. Plausible?

At the 2005 SHOT show I had a conversation with the project manager of the .460 XVR. He informed me that the reason for the gain twist was to keep bullets from skipping the rifling�I�ll have to take his word for it.

I don't see how there would be. There is angular inertia that has to be overcome, and you are just choosing a different place to overcome that. I don't think there is any effect on friction. Friction is just the force (bullet pressing against barrel) times coefficient of friction. I don't think twist rate has any effect.



It doesn't seem so to me, but I was wrong once before. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

We know that higher pressure will create higher speeds. We do not know whether gain twist rifling does any such thing. So far, the explanation requiring the fewest assumptions is the pressure explanation. If someone takes the time to do the pressure measurements, maybe we will get a definitive answer.

I guess one way to phrase my question is this: Is there any known difference in muzzle velocity between a 1:10 twist and a 1:12 twist, all other factors equal? If not, then why would there be any difference in muzzle velocity in a barrel that transitions from one to the other?

Well, for better or worse Harry Pope's rifles used a gain twist. Whether that's why they held records that stood for decades or not, who knows?

I believe that was the original 1891 versions. I'm thinking the gain twist in that case was intended to solve some throat erosion issues but I may be completely mis-remembering this.

I had a gain twist barrel once. In the late 1990s Steve Webb of Apex made me one--cut rifled. It started with straight rifling and ended up in the 1x9 range. It was chambered in 338 Win mag.

I talked a lot with Pat Eddinger who had tested a few of Steve's gain-twist barrels. The one that started with straight rifling was the "radical" gain twist. The other option was one that started with some twist vs straight rifling.

The idea was the initial area of straight rifling would reduce resistance and allow the bullet to accelerate more quickly. The problems with the radical gain twist were the stress it put on the bullet as the twist increased. Pat said Barnes X bullets did not work in this type of gain twist because they would shed copper as the twist increased. A conventional bullet supposedly has enough flex between the core and the jacket to allow it to accelerate in a gain twist barrel without deforming the bullet.

What really sold me was when Pat shot a gain twisted 416 Rem. It would shoot factory ammo at 2500 fps, which is 100 fps more than published.

Well, my 338 Win with the radical gain twist didn't shoot any faster than a regular 388 Win. It's accuracy wasn't any different either. I finally gave up and got rid of the rifle.

Interestingly, both my current and my last 416 Rems with conventionally rifled barrels shoot factory ammo at 2500+ fps.

I am not sure the gain twist is the magic, just like I am not sure there is anything special about 3 grooves vs 6. I think the idiosyncracies of the individual barrel have more to do with increased velocity than gain twist. If I were going to try another gain twist I'd not go with the radical version.

And no, my 1K BR rifle does not have a gain twist barrel,and neither does anyone else's rifle on the line--though mine is a 3-groover. I can promise you if gain twist barrels consistently added 100-200 fps and shot well we'd all have them.

FWIW I just went into my old reloading records to try and get some comparisons on velocity. I've had two 338 Jamisons, one with the uniform twist @1:10 and the other which I still have, a gain twist supposedly started at 1:16 and went out at 1:11. How he could be that precise I don't know and I doubt he can. Both barrels were 21", as they were in all the rifles I had in those cartridges.

I could quickly only get my hands on one load combination using the same powder and the same bullets in a uniform twist 338WSM and the gain twist 338 Jamison. Both rifles had 21" barrels. The water capacity of the two cases was within 2g of each other, the Jamison using a RWS case having capacity of 81g and the WSM WW case a capacity of 82g. The rifles both weighed just a tad over 7#.

Using a 210 Nosler Partition fired over an Oehler 35P and Hunter as the propellant, they both used 72g of powder for average velocity of 2845 fps out of the Jamison and out of 1:10 Pac-Nor averaged 2860 fps. One grain more @73g indicates the bolt was heavy for both.

My loading record doesn't tell the ambient temperatures at which these were shot, but my recollection of virtually every combination of powders and bullets I tried was that they shot the same in similar conditions. While I have a Pressure Trace setup now and still have the Jamison, unfortunately I sold my last 338 WSM a couple of months ago so I can't make any direct comparison with that system.

At least in my case there wasn't a nickels worth of difference in velocity and they were both about equal in accuracy average just under MOA with preferred loads.

My 30 cal is 1 to 30 ending at 1 to 10.The 7 is 1 to 30 ending at 1 to 9.Both of mine are fast movers.

I am personally familiar with two rifles that use gain twist barrels, both from Ron Smith.

Certainly realize that a sample of two is not statistically significant, however both rifles get well above average velocities.

A good friend of mine had a Husqvarna in 7mm Rem Mag rebored by Ron to 358 Norma. The rifle gets just under 3000 fps with 250 gr bullets and 70 gr of 4350. I have had five 358 NMs over the past forty years and none of them have ever come close to that.

Ted

Steve....Pac-Nor was involved in making gain-twist barrels for a short time but as I understand it there was a liscensing problem with the equipment so he stopped.

I have two of the barrels he made in 30-caliber. Barrels are both 24" long and have an initial twist-rate of 50-1 and end up at the muzzle with a twist-rate of 10-1. One is still a blank but the other was contoured and chambered in 7.82 Lazzeroni Patriot and like you I have found it rather easy to exceed expected velocities across the board .... and I've found that while it really shoots the 165gr, 180gr and 300gr bullets exceptionally well it will even do a "good" job using 130gr bullets lauched at substantial velocities..... haven't shot anything with the 130gr yet but I suspect it will be destructive. My 24" barrel will run a 165gr Nosler Partition faster than a 26" barreled Weatherby I've seen ---- at least over my Oehler chronograph. I haven't done a lot of work on the heavier bullets but I suspect they will also outshine a "Roy".

There isn't any free-lunch as you do need to add more powder but the lower pressures you get with the slower twist-rate near the chamber allow you to get away with this without spiking pressures.

The only thing about the barrel is that while it doesn't foul very much (very, very smooth interior finish) but when you run a rod thru it the rod tends to "skip" and not follow the grooves/lands.

Well, so far we have a lot of posters who notice no difference, some who talk of a velocity increase but don't tell us what it is, and one grammatically-challenged poster who talks of a 200 fps improvement.

Here's the nail in the gain-twist coffin.

Since around 1900 shooters have competed in 1000 yard matches at Camp Perry. They have included some of the best shooters in the world. They have included some of the best experts, like Homer Powley, Father of American Ballistics. They have gone from big magnums down to 6.5-284s and even won one long-range championship in 2004 with a 6mmXC.

If there were the SLIGHTEST MEASURABLE improvement available in velocity from gain-twist, they would use it because extra velocity helps wind deflection and just one shot 1/2 inch farther out can cost these guys the match.

They don't use gain twist.

When David Tubb set out to design the best possible match rifle for ranges from 200 to 600 and sometimes 1000 yards, he spared no expense. His "mass produced" rifle pushes $5,000 with sights. He didn't use a gain-twist barrel.

I think that nails it.

Another poster asked if there were any velocity difference between 10" and 12" twists. There should be if gain twist works. There isn't. It doesn't.

Those who think, based on a sample of one or two, that their gain-twist produces 100 fps or so extra velocity are merely experiencing the normal variations from barrel to barrel.

How is that?

because the elapsed time between muzzle and target is shorter, and therefore is exposed to wind drift for a lesser time.

And if anyone wants to experiment with one, I have a RKS gain twist barrel in 284 chambered and fitted for a Sako L579 with low low miles.

Your 4th and way long better punt.It's funny a respected gunwriter experience mirrors mine but as owners were wrong.

This isn't worthy of any more of my time.Go read some more books.I hear Tubb got a new one.......laffin

I've had two Ron Smith 338 barrel with std 10" twists, and a friend has another. All three had no problem getting full ballistics and were accurate. The gain-twist 284 barrel was accurate but did not show any greater velocities than expected from a 22" 284 Win, and I loaded it to where I was getting definite pressure signs (compressed loads of RL19 and 4831 with a drop tube), so it wasn't a matter of underloading. IIRC it was 1:20 to 1:9

DB,

The article I wrote on the .25-'06 is dated April 1995. Considering the lag in publishing in a quarterly magazine and fitting the barrel, Chris probably made my barrel sometime in 1993.

I had a 700 custom in .338-06 Ackley that was made by a kinda-famous gunsmith in South Carolina that was generally screwed up. I forget who called me, Darrell Holland or Chris, but the barrel was gratis, just to see how it shot.

The story I got is that the barrel was a mistake; somehow it turned out to be a gain-twist. When Chris discovered it, he sent it to Barrel-Scan Inc. and the twist-rate was absolutely linear, starting with 1:11" at the breech and ending with 1:9" at the muzzle. I still have the Barrel Scan chart and it is just a perfect straight line.

When I wrote the article, I didn't get all tangled up in the gain-twist thing. I simply wrote it as full-feature (5,000 words) .25-'06 article; Neidner and all.

A couple of years later, I met Chris in Brusett, Montana; he was coming out from hunting deer and I was going in (he shot a bonzo whitetail). I mentioned that the gain-twist Pac-Nor was shooting up a storm and was one of my favorite rifles.

He told me (again) that the barrel was a total mistake, basically a gear malfunction, and that he was delighted that it shot so well. He commented further that "I could not make another like that one if I tried, but it turned out so darned well that I wanted to know how it shot."

He told me at the time that he had since gotten the gear to (purposely) cut gain-twist barrels and was going to start production in the not-to-distant future. I believe it is these "production" barrels that you are talking about.

I really don't have a dog in this fight. I've only shot a single gain-twist barrel, my "mistake" Pac-Nor .25-'06, and it is phenomenal.

In my experience, there are two types of barrels; boy barrels and girl barrels. The girl barrels are picky and bitchy; they whine and moan and are totally pissed if you don't give them the exact perfect load. Boy barrels are calm and easy to get along with; shooting most loads at least acceptably and many loads in a superb fashion.

My Pac-Nor gain-twist .25-'06 barrel is definitely a boy barrel.

Steve