Variable Twist Rate - Engineers Speak Up

[Werewolf]

I just read that the new 460 S&W uses it.

Most engineers are pretty smart fellows and they rarely do something just for the hell of it. I wonder why they chose to use gain twist in the new S&W 460?

Anyone know a S&W engineer they can pump for info. That would be interesting to know.

 

[benEzra]

Because in a revolver, the bullet is already moving at a good clip before it hits the rifling (since the cylinder and forcing cone are smoothbored). In the .460, it is moving so fast by the time it hits the rifling that jacket stripping could occur. Hence gain-twist rifling, to get the bullet spinning more gradually.

 

[Vern Humphrey]

Because in a revolver, the bullet is already moving at a good clip before it hits the rifling (since the cylinder and forcing cone are smoothbored). In the .460, it is moving so fast by the time it hits the rifling that jacket stripping could occur. Hence gain-twist rifling, to get the bullet spinning more gradually.

Could be. On the other hand, the .44 magnum, the .454 Casul and similar rounds don't have progressive rifling and don't seem to suffer from the lack.

 

[VARifleman]

Could be. On the other hand, the .44 magnum, the .454 Casul and similar rounds don't have progressive rifling and don't seem to suffer from the lack.

Check the velocities of those rounds compared to the .460. The velocity of the .460 compared to the .454 is 400 ft/second higher. That can make quite a difference.

 

[Jim Watson]

Colt cap & ball revolvers had gain twist barrels.
Harry Pope rifled his schuetzen barrels with a gain twist.
Both certainly worked well in their respective areas, but good quality constant twist barrels did, too, and are a lot less expensive to make. I figure S&W would have used constant twist if the .460 would have run with it.

 

[Vern Humphrey]

Let me see if I can get this to work:

For the .454 Casul from the Hodgen website

260 GR. FA JFP COL: 1.765"
H4227 33.0 C 1762 42,100 CUP
H110 36.0 1954 51,600 CUP
LIL'GUN 35.5 1895 37,900 CUP

For the .460 S&W from the Hornady website:

ammo description muzzle 50 yds 100 yds 150 yds 200 yds

460 S&W 2200/2149 1948/1685 1715/1305 1504/1005 1322/746

It seems like the difference is around 100 to 150 fps.

Now, you may be right -- but I suspect if there is a bullet problem it's because the bullets are being over-driven.

 

[VARifleman]

1950, the highest of the velocities that you listed for the Casull is 250 ft/sec slower than the muzzle velocity listed for the .460.

I don't have hodgen's manual, but on ammoguide:

.454 casull with a 185

1742
1762
1929
1946
1988
2142

.454 casull with a 225

1555
1716
1759
1857
1903
2014

.460 with a 200 gr bullet (the nominal performance listed

2300

 

[Vern Humphrey]

The Hornady website gave .460 velocity as 2200/2149, which on the lower side is only 5 fps faster than the .454 Casul with a 185 grain bullet(at 2142fps) and only 135 fps faster than the .454 Casul with the 225 grain bullet (2014 fps.)

Even if we take 2300 fps as the .460 velocity, we only have a difference of 158 fps over the fastest .454 load.

 

[VARifleman]

The low velocity of each is not what we should be concerned about, but the high side. The bullet hitting the rifling at its fastest speed at that point is the one that as an engineer you need to design for. They assured it wouldn't have a problem by using gain twist rifling, which may or may not have been for the sole purpose of saying that they designed something that's different than everyone else.