Uncles new gun? With a twist!

04 November 2008, 21:59

My wife's uncle is getting his old custom rebarreled and was asking some interesting questions. He was unsure of the chambering at this time but was asked if he wanted to go with a 'gain twist' bbl. He was told more speed and less bbl length so he could have a 22" instead of a 24" with the same speed. I have never heard of this and thought 'snake oil' but did some searching anyway.I figure the guys on here have had something good or bad to do with these and could help me help him before he lays down his cash.
I figure changing the rate of twist would cause fouling as you are disrupting more jacket material. I cant see how this is better for accuracy to have a more 'mangled' bullet? I have heard of a few people up here with these bbl's but haven't heard if they are worth it or not.

04 November 2008, 22:29

GeorgeS

Gain twist doesn't increase bullet velocity; the bullet's rotations per second increase as it travels down the bore due to the increasingly faster twist.

He can just go with a barrel with a faster twist to begin with.

Gain twist was more common with blackpowder, and doesn't seem to improve accuracy in smokeless powder cartridges (according to Dan Lilja).

George

06 November 2008, 07:34

PoppaW

I guess he called the guy who is building his gun and he has 17 gain twist bbls on guns. Or something like that. So he said he's gonna try one so I guess when its done I get to see one up close and maybe shoot it and put it over MY chrony to see WTF it really does. Should be fun.

06 November 2008, 21:30

MileHighShooter

I do believe the S&W 460 XR and possible the 500 are gain twist

07 November 2008, 06:34

.366torque

quote:
Originally posted by PoppaW:
My wife's uncle is getting his old custom rebarreled and was asking some interesting questions. He was unsure of the chambering at this time but was asked if he wanted to go with a 'gain twist' bbl. He was told more speed and less bbl length so he could have a 22" instead of a 24" with the same speed. I have never heard of this and thought 'snake oil' but did some searching anyway.I figure the guys on here have had something good or bad to do with these and could help me help him before he lays down his cash.
I figure changing the rate of twist would cause fouling as you are disrupting more jacket material. I cant see how this is better for accuracy to have a more 'mangled' bullet? I have heard of a few people up here with these bbl's but haven't heard if they are worth it or not.

You are talking about the Ron Smith barrels, correct? I've heard the theories as well. I heard the extra velocity comes from the first part giving less pressure, so you can load higher. I've never seen it proved or disproved. It'll be neat to see what you guys find.

07 November 2008, 08:45

Rodney H.{500Jeffery}

I believe some of the original Weatherby rifles had gain-twist rifling- I may be mistaken on this. Gain-twist is where the rifling starts slow and progressively gets faster right? Rodney.

07 November 2008, 10:09

PoppaW

Yes a slow twist to start then getting faster. I guess its all up to the buyer at what they start and finish at. He had a 28" bbl before and will be using a 22" this time. I can't wait to see what the velocity is on this thing. If he lets me near it that is!!!

07 November 2008, 10:17

RIP

I know some 1000-yard championship .338 Lapua Mag. rifles have gain-twist rifling that finishes up near the muzzle at 1:7" twist.

They use .338/300-grain bullets that are about 2.5" long, IIRC.

It makes sense that starting at slow rate of twist and finishing fast might improve accuracy, if you need that fast terminal twist for the long bullet.

Straight 1:7" twist is required for those long .338 bullets too, the minimum required accuracy twist, if gain twist is not used.

I think the effects on pressure and velocity will be negligible.

If I built another .338 Lapua, I would want one of those gain-twist barrels.

I don't recall Roy Weatherby using gain-twist barrels, but he probably did at one time, then found he could make more profit and get same performance from his cartridges with standard rifling.

07 November 2008, 10:18

Macifej

quote:
the effects on pressure and velocity will be negligible

Yep...

07 November 2008, 10:24

PoppaW

The bbl is here and 22" so I guess his velocity will be lower than what he was used to.

07 November 2008, 20:30

BaDonkaDonk

Hey PoppaW,
What is the reason for the shorter barrel? He was willing to give up velocity of a 24" bbl for a 22" bbl for what gain? Or is he just tinkering.

09 November 2008, 14:16

PoppaW

He was led to believe the gain twist in a shorter bbl length will shoot just as fast. We will see if this is true. I think his choice of 22" is too short even if he does get some gain. But it's not my money being spent so what do I know