Gain twist rifling what is it, the purpose,

[tdiem52]

Would someone explain gain twist rifling.

 

[BrownBear]

It starts slow at the breech and gets faster as you go toward the muzzle. Supposed to be better than sliced bread back in the day guys were promoting the idea and selling the barrel. Kind of a flash in the pan, a one-day wonder.

Kinda scarce today, which tells me something. :wink:

 

[bob308]

it starts out slow say 1-70 then gets quicker as it goes up the barrel maybe 1-48 at the muzzle. that is just an example. pope cut his barrels with gain twist. the Italian military rifles of ww1 and 2 had gain twist.

that was the easy part. now some will say it shoots better I have never seen a gain barrel out shoot a straight. I have cut both.

 

[mooman76]

I have heard some(very few) did actually shoot very well but most did work out as hoped so they weren't worth the effort. Theoretically it sounds like a good idea.

 

[azmntman]

I have heard some(very few) did actually shoot very well but most did work out as hoped so they weren't worth the effort. Theoretically it sounds like a good idea.

Well every once in awhile one will get a production gun (or car etc.) that just shines. I have a few, a CVA.50 that will shoot 1-2 inch group all day long at 90-100 yds. Not many of my (many) other guns will do that consistently. I gotta a car too that with 325K on it has had only an odometer and 4 headlights, runs like new, plenty of HP left, no leaks anywhere and still gets more MPG than it was rated to when new.

Yep Im' keepin em both!

 

[galamb]

The "theory" is that it should should a variety of projectiles "well".

So if you want to shoot round ball the twist starts out slow and as the twist increases there is resistance on the ball allowing for a more even pressure curve without overly rotating the ball.

Additionally, the resistance will help consume all the powder "within" the barrel so you are not handicapped by using a shorter barrel (less un-burnt powder blown out the end) - more efficient powder use, which could mean that you can use less powder to achieve the same results as a longer barrel with a slower twist (but that is generally true with any faster twist barrel/roundballs) - the less powder part anyhow.

The second advantage is supposed to be that the (final) faster twist will help stabilize longer projectiles so you could shoot a long plains bullet with the same type of accuracy that you would get from your round ball out of the same barrel.

Does it actually work? maybe - if it was better/stronger/faster then it would probably be the way that all barrels are made today (this is not a new invention by any means).

Since it has mostly fallen to the wayside as a rifling method could be 1) because it's more time consuming to produce 2) it really "doesn't" provide any great advantage or 3) a combination of the two - not enough improvement to justify the extra work (at least in the black powder world).

I have experience with ONE gain twist rifled barrel.

It is a Colerain that an acquaintance owns. It is a 50 cal barrel rifled 1:96 at the breech moving up to 1:48 at the muzzle.

And while it's a bit of a conversation piece at the range, and it is "accurate enough" we have never found it to be any more accurate than a (standard) 1:48 twist, which likewise shoots both conicals and roundballs "well enough".

If you want one for the "uniqueness" or the "cool factor" it will probably serve you well.

But if you want one because it will be a "super barrel", save the premium cost (and the wait time). Time at the range with extra powder and balls (or conicals) will do far more to improve your accuracy than any "barrel voodoo".

 

[M. De Land]

Here is the deal about gain twist barrels I learned from ready Cliff LaBounty and why they can be superior in accuracy if made with precision like Harry Pope did.
Very few could cut a gain with the precision Pope could which did result in better accuracy than most even twist barrels of his contemporaries.
The groove in a right hand gain twist barrel gets narrower as the pitch increases toward the muzzle.
I can explain this but it takes awhile. Basically the cutter head moves more side ways as the angle increases thus narrowing the groove and widening the land.
This occurs because the face of the cutter (scrape or hooked) is set at an angle of about 10-15 degrees to the line of the bore. The greater the helix angle the narrower the cutter face engauges the barrel wall.
If the cutter is turned to the left, the opposite happens in that the groove becomes wider and the lands get more narrow as the pitch increases.
The old timers called this choking and was different than lapping a diameter change, making the muzzle diameter tighter than the breech.
This widening of the lands toward the muzzle increases bullet and to a lessor degree ball, resistance in the bore which is tantamount to tensioning the barrel toward the muzzle.
Recoil is pushing the barrel backwards against the breech plug and bullet increased resistance is pulling the barrel forward. This tensioning in opposite directions tends to dampen barrel oscillation (barrel movement from flexing) so the muzzle does not move as much out of line with the aiming point.
Pope always used gain twist and usually left handed to put the torque into his cheek being a right handed shooter.
Most gain twist barrels will shoot a bit slower than will even twist of the same length and caliber.
They cannot be hand lapped with a lead slug because of the pitch or helix angle change. They can be lapped with leather washers though.

 

[mhb]

Some notes:

1. The groove in a gain pitch barrel decreases in width as the pitch increases, and this is true when the face of the hook is at 90 degrees to the body of the rifling head, or angled toward the direction of the pitch, which is the usual geometry. The reason for the change in groove width is the change in aspect angle (angle of advance) of the hook with respect to the direction of the groove. The groove would only be wider toward the muzzle if the hook designed for the opposite direction of twist were employed, and that is not the usual practice.
2. Harry Pope customarily made his breech-muzzleloading barrels with gaining pitch, for use with cast lead bullets. In fact, this is something of a mechanical cruelty for the bullet, and worked so well only because of the plastic nature of the bullet material, since the bullet had to engage at the muzzle with the fastest pitch, and deform the bullet body to conform with the changing pitch and land width on its way to the breech; then reverse the process under the stresses of firing - the result was shearing force applied to the bullet surface in both directions. Pope also made breech loading match barrels with fixed pitch, some for high power rounds, and they shot as well as his gain-pitch ML barrels. I believe that the secret was in Harry's careful workmanship, and not the direction, form, or gaining pitch of his rifling.
3. Left-hand rifling causes the torque generated in firing to twist the rifle to the right, away from the (right-handed) firer's face.
4. Choke in a rifle barrel is a result of decrease in the bore diameter near the muzzle, whether lapped or produced by other means: it has nothing to do with change in land or groove width.
5. The difficulties in producing a gain-pitch rifled barrel are not outweighed by any gain in accuracy, assuming equal workmanship and quality control: the most avid pursuit of the ultimate in rifle accuracy is in the benchrest arena, where you would be absolutely unable to come up with a rifling scheme or geometry which has not been thoroughly tried, and where gain-pitch rifling does not and has never competed successfully with fixed-pitch. The BR community will try anything, but won't use anything that doesn't win consistently, and the barrel makers whose products win consistently are very good, indeed.

mhb - Mike - barrelmaker, ret.

 

[crockett]

Thanks all for those great explanations. I never knew the groove width decreased towards the muzzle, I thought the only change was the twist of the rifling became faster.
I'm not sure what the intent was on the gain twist. I thought the projectile more easily entered a bore with a slow pitch and then the pitch increased to stabilize the projectile.
I was under the impression the groups fired from such barrels weren't that much better but I could be wrong on that.
While the theory is good I have wondered what such rifling changes do to a projectile as it travels down the bore and is continually changing to obdurate to the rifling.
Pretty interesting subject that I really don't know much about.

 

[M. De Land]

Ron Smith of BC Canada is making some excellent gain twist barrels currently used in BPCR competitively around the world.
I have a friend that shoots several of his barrels.
An other advantage of gain twist barrels when using a paper patch bullet is that the helix gain helps in patch break up and uniform expulsion at the muzzle.English rifle experimenter Metford discovered this.
I have always been amazed that it works so well in bullets an inch and a half long as the nose is always trying to out spin the base.
Question: does gain twist torque greater in the direction of the twist or away from it as bullet resistance increases because of land width gain?
It has never been proven definitively that gain twist is inherently more accurate than even twist but it does seem to be catching on in Schutzen and long rang paper patch bullet use.

 

[M. De Land]

Pope did make even twist barrels for customers but always used gain for his personal match rifles.
He settled on the 32-40 case necked up to .33 caliber for his personal use in later years as he switched over to breech seating grease bullets from muzzle loaded strip patched bullets.
Pope lapped in a full barrel taper using a series of one inch long gauges that dropped in to measure the taper gain, according to Smith's book on Popes barrels.
I lap choke in bores but prefer to lap level and choke the last three inches or so.
This was the method used by many of Popes contemporaries like Horrace Warner or Norman Brookway which made fabulous barrels themselves.
Pope made and fit the match barrels for the US shooting team one year.
The governement gave him a set of specifications he felt were wrong and told them they either took the barrels the way he designed them or not at all. They gave in and won the international match that year doing it just the way Ole Harry told them to.

 

[robinghewitt]

I have a notion the Remington NMA was gain twist. OTOH just because something is in my head does not make it true :surrender:

 

[Col. Batguano]

Has anyone done the calculation regarding the amount of torque generated or free recoil toward (or away from based on rifling direction) your face is generated with the average rifle?

I'm betting it isn't much, but physics say that it IS something. If it were significant, they would make left handed barrels with different twist directions than those intended for righties.

 

[M. De Land]

I just don't know for sure as I've heard it both ways but here is my thinking and feel free to challenge it because I want to know the truth.
I understand Newtons law that for every action there is and equal and opposite reaction, in this case the bullet wanting to "unscrew as it were" from the barrel twist it is forced to follow but in a gain twist barrel the bullet is meeting with increased resistance because the land width is growing.
This increased resistance is why gain twist barrels shoot slower than even twist because the expansion ratio of burning powder is increasing and the pressure is dropping with the increase of volume.
On the other end of the fulcrum the bullet is meeting with more resistance and presumably pulling the barrel with it as the friction increases.
If this is correct(increased friction over coming helixial recoil inertia, than the left hand twist of a gain twist barrel would torque into a RH shooters cheek.
This is my understanding of the main reason why Pope used left hand gain twist in his personal rifles.
It doesn't make any sense if it torqued away from his cheek as far as I can see as torque control is one of the reasons for a comb on a stock.
Good shooting requires a firm check weld to the stock comb to control torque and enhance accuracy.
As the range increases this becomes more obvious in where the shots print on target.

 

[William O.]

Excellent discussion and explanation! Great question too of course.

 

[mhb]

The torque resulting from a bullet passing through a rifled barrel causes the barrel, and the rifle, to be rotated in the opposite direction from that of the rifling itself; thus, the bullet's direction of rotation. This is true whether the rifling changes in pitch or not. A familiar demonstration of this effect is the use of an electric drill: the body of the drill attempts to rotate in the direction opposite to the drillbit's rotation, and the force increases as the resistance to the drillbit's penetration/forward motion increases.
In flight, the bullet will drift in the direction of rotation, due to aerodynamic forces on the bullet, which effect becomes more significant at increasing ranges: this is the reason why some U.S. military rifle sights (Buffington, 1901 Krag, 1905 Springfield, etc., in service during the era when long range massed musketry fire was considered important) incorporate a compensating offset to correct for the drift at long ranges.

mhb - Mike

 

[M. De Land]

Yes, we have tables for spin drift even at mid ranges of 600 yards and it becomes increasingly important at 8-9 and 1000 yards with these big lead bullets ,moving at subsonic velocity past 300-400 yards.
Transonic ( 900 to about 1300fps) is where they get the most buffet to there rotational stability.

 

[Rifleman1776]

Excellent discussion and explanation! Great question too of course.

Yes it is.
Gain twist, like so many ideas in the history of firearms was just that, an idea. If the idea really had proven to have benefit we would see a lot more barrels like that. But it proved to be just another historical oddity and fell out of style.

 

[hanshi]

I can't speak scientifically about gain twist or even say it may or may not have advantages over uniform twist. What I can talk about is this:

Back in the mid 1960s I ordered an H&A Heritage, a .45 underhammer rifle. I also had the choice of a barrel with uniform twist or with "gain" twist. I just threw the dice and chose gain twist. When received the rifle was a well made and crafted underhammer rifle. It was apparent from the beginning that this rifle was acc-u-rate! I now own a few very accurate ML rifles. They are capable of finer accuracy than I can wring out of them. But I've never owned one above .36 that can surpass the accuracy of that 50 year old caplock. It's been used long and hard and is now retired. The bore, however, is still pristine.

 

[Rifleman1776]

I used to sell the H&A undies and my family shot with them. They were both affordable and accurate. Can't say any were gain twist though.