Hello the camp:
Does anyone know anything about the "gain twist rifling" used in the new S&W .460 XVR?

It is a new one on me but looks interesting. It may be a good way to stabalize a large bore projectilw. It would seem to work by starting the spin gradually and spinning it up down the barrel. Or it may not work at all. But it looks cool. And sometimes that is better than it working?

There is an article in "Handloader" about the 460 S&W. Just wondered if anyone had seen it.

Judge Sharpe

I've done some thinking on gain twist rifling but only on it's use in a long gun.
If you took the rifling marks with a 1 in 16 twist barrel and you compare the same in a 1 in 7 twist barrel they would not be the same of course. But when you fire a rifle with the 1 in 16 and it comes out as a 1 in 7, something has got to be bent or twisted or whatever but......
I don't know something just seems like it would get screwed up.

it has veen around since the muzzle loading days and a very few people still like it today. The people I knew who used it were cast bullet rifle shooters.

The Ballard Rifles in Cody Wyoming (hope they're still in business) used it but I never understood, the bullet starts at 0 feet per second so the standard continuous twist starts turning the bullet at 0 RPM and a couple inches down the barrel the bullet has some velocity and a cooresponding increase in RPM.....as you see the standard twist IS gain twist and to confuse it with a (supposed) gain twist in the barrel has never made sense to me.

Standard traditional barrels have produced marvelous groups and I can see no reason for "gain twist" except for traditional replication.

The original "New Model Remington" Model of 1858 44caliber revolver was made with gain rifling

As were some of the post civil war Remington Revolvers.

AllanD

didn't the carcano use it?

duikerman, gain twist is about the TWIST not the bullet rpm.. that is, "twist" is a constant X per Y, while gain twist decreases X per Y over the barrel length

jeffe

quote:

Originally posted by jeffeosso:
didn't the carcano use it? Jeffe, I didn't think so here.

duikerman, gain twist is about the TWIST not the bullet rpm.. that is, "twist" is a constant X per Y, while gain twist decreases X per Y over the barrel length

jeffe

I'm perfectly aware of what gain twist is but thanks for the lesson. My reply was specifically to this remark from the thread starter Judge Sharpe:

quote:

It would seem to work by starting the spin gradually and spinning it up down the barrel.

and my point is that traditional standard twist does exactly this perfectly. It starts the bullet turning gradually and increases the (RPM) twist as the bullet increases in velocity.

It's not the case that the bullet in traditional twists start their RPMs at 200,000 RPM instantly although the time it takes to get there is incredibly little.

I've always found the gain twist idea to be interesting but could never find a good reason for it and as mentioned there's a conflict in the rifling marks that must be left on jacketed bullets that continuous twists don't have.

Pope"s barrels were gain twisted.

Dave

Yeah, the old M91 Carcanos had gain twist.

DM,
i think we both understand that RPM changes over speed... but bullets reach MOST of their speed in the first 10 inches ... but calling twist "gain twist" over changes in velocity, not twist rate can just lead to ME being confused!!

quote:

Originally posted by jeffeosso:
DM,
i think we both understand that RPM changes over speed... but bullets reach MOST of their speed in the first 10 inches ... but calling twist "gain twist" over changes in velocity, not twist rate can just lead to ME being confused!!

Jeffe,
I didn't mean to confuse things here. It was merely my premise to point out that the supposed real advantage in gain twist is already had in conventional continuous twist and nothing more.

Again, I have nothing at all against gain twist but just don't see an advantage in it. Further with jacketed bullets it's likely a defecit.

Someone mentioned Pope's barrels had this feature but someone please correct me; wasn't this exclusively used for cast bullets?

Don't think his target rifles had gain twist, but they had a choke effect, that is, he lapped them, so the bore was .001" or so tighter at the muzzle. Gain twist is good for round ball loads cast from soft lead, so the rifling doesn't overstress the lead. Also his rifles were designed for seating the bullet in the rifling with a special tool, and the case only had powder, and a wax wad.

It seems to me that as the twist rate changes the helix angle of the rifling has to change thereby causing more deformation of the bullet.

The gain twist barrel will deliver higher velocity since the rifling is straight for the first several inches as the bullet gains most of its velocity, then starts twisting to deliver the rotational force needed to stabilize the bullet. Since S&W is trying the make the 460 the velocity king of revolvers, they went with a gain twist rifled barrel.
Gain twist will deform a bullet more than a straight twist barrel, but it isn't too bad with short pistol bullets and their fairly slow final twist (1 in 16"); it would be much worse with a long bearing design rifle bullet trying to use a final twist of 1 in 10".

Have you ever tried to lap a gain twist barrel?
Butch

quote:

Originally posted by butchlambert:
Have you ever tried to lap a gain twist barrel?
Butch

What a pain, you'd have to use a new lead lap for every pass through the bore.

quote:

Originally posted by CMcDermott:
The gain twist barrel will deliver higher velocity since the rifling is straight for the first several inches as the bullet gains most of its velocity, then starts twisting to deliver the rotational force needed to stabilize the bullet. Since S&W is trying the make the 460 the velocity king of revolvers, they went with a gain twist rifled barrel.
Gain twist will deform a bullet more than a straight twist barrel, but it isn't too bad with short pistol bullets and their fairly slow final twist (1 in 16"); it would be much worse with a long bearing design rifle bullet trying to use a final twist of 1 in 10".

Yes, in the original percussion revolver it does distort the ball more by intention, but reduces the "unintentional distortion"

The bullet in a revolver, ancient percussion revolver or otherwise has several times the bullet jump of any rifle, so a gain twist reduces the "shock" of engaging the rifling
after the relatively long freebore in the revolver cylinder forcing cone and then the jump across the cylindergap and into the "leade" of the barrel proper...

Under ideal circumstances revolvers are abusive to bullets... anything to reduce that has just gotta help....

AllanD

quote:

Originally posted by Fjold:

quote:

Originally posted by butchlambert:
Have you ever tried to lap a gain twist barrel?
Butch

What a pain, you'd have to use a new lead lap for every pass through the bore.

And I'll bet you a cup of coffee you wont be able to make even one pass with your lap!!

At the risk of screwing up the thread, I'll put in my two cents worth sunce I do have some experience with gain twist barrels and some slight knowledge in the field.
Pope did make gain twist barrels and considered the gain twist to be an important part of his breech/muzzle loading match rifles. Later, he used a uniform twist for jacketed bullet rifles.
Most gain twist barrels are cut though i have heard of some gain twist barrels made by button rifling. The button must have been specially designed and either the barrel or the button turned via a CNC setup.
Anyway, gain twist barrels offer theoretical benefits as well as some real ones. The higher velocity claims made for them have never really been proven. If such an advantage truly exists, it may be as much due to better sealing (the one real benefit I can think of) as to reduced pressure required to spin the bullet.
I have lapped gain twist barrels. It was necessary to keep the lap a little shorter than usual (about 1" long). After the lap went throught the barrel once, the lands on the lap (corresponding to the grooves in the barrel) were narrower at each end and full width only in the middle. The lap subsequently worked well and did the job required of it.
I presently am shooting three gain twist barrels. A 6mm (11.8 to 7.8), a 6.5 (12 to 7.5) and a 30 cal (16 to 13.5). All were made by a friend, Ron Smith. All have performed very well for me. Do they work better than uniform twist barrels? Well, no. The 6mm (in 6BRX) does produce impressive velocities but this is true of most 6BR's regardless of barrel type. The others don't do anything I didn't expect them to do.
I don't believe in using a barrel with a radical gain. I prefer to gain only about 1?3 or less (12 to 8 for instance).
Real advocates claim higher velocities, better barrel life, and lower pressures but, to my knowledge, such claims have never really been proven. Regards, Bill.