Gain Twist

[BigG]

Help me out here I started thinking about this and want to know what others think...

Gain twist is one that starts out slow and accelerates as the bullet passes thru the bore. Colt's BP revos had this as they fired a round ball whose short bearing surface might cause it to strip otherwise.

The thought I had was this: Suppose you start the bullet out at a slow twist and increase the angle as you approach the muzzle. Does the bullet continue to increase its twist until it strikes the target or does it somehow stabilize at a predetermined optimal twist? My guess is it continues to tighten the twist but what do I know?


Discuss, please.

 

[brickeyee]

If it does not strip it will not continue to accelerate once it leaves the barrel. The muzzle twist rate will be the final rate (again without stripping).
Gain twist has been used off and on for many years in experiments. I have yet to see any really good evidence it provides a significant advantage with modern projectiles. The lower engraving force might have some slight advantage.

 

[Brian Williams]

Physics would not allow a continued acceleration without continued intervention on the object in motion. The twist at the muzzle will determine the rotation while it is in flight, At least the start of the flight because of the friction of the air will be acting to slow it down.

 

[Moonclip]

Any modern guns have gain twist besides a custom job? Only gun I was ever aware of having gain twist was some versions of the Italian Carcano rifles. I have never heard of a gain twist handgun until now.

I always thought it was a sound idea, it is suppose to promote longer barrel life. When the Carcano came out it was suppose to be a big deal and a state secret I think that the rifle had a gain twist barrel.

 

[JohnBT]

The S&W 460XVR (X-treme Velocity Revolver) uses a gain twist barrel.

John

 

[swampsniper]

I shoot a gain twist barrel on my .45 frontstuffer I built around 1975. It came from Numrich Arms. It has been a great barrel for round balls, not bad for anything else I've tried. As for accelerating spin after leaving the bore, does your car keep on gaining speed after you get off the gas?

 

[Fatelvis]

I always thought the different rate of twist would leave a "sloppy" indentation in the bullet, kind of like threading a nut down a bolt that has changing threads per inch. It would eventually strip out the nut. Just my feelings.

 

[esheato]

SVI race pistols have the option of the AET gain twist barrels.

Ed

 

[Standing Wolf]

I wonder how the rifling is cut.

 

[Jim K]

While the Colt percussion revolvers could be fired with round balls, in service they were loaded with cartridges using picket bullets. I have no idea what effect, if any, the gain twist had on the pointed bullet, but it had a short bearing surface. Anyway, none of the other makers used gain twist, so I expect any benefit was theoretical or mainly in Colt's mind.

Jim

 

[MikeJackmin]

I recall reading that the Italians were pretty excited about gain twist in the rifles - they saw it, perhaps correctly, as a means of minimizing barrel wear. They believed the resulting improvement in the service life of their rifles was significant enough to justify the added cost.

I have no opinion, but I assume that this is something that would have been fairly easy for them to test, so perhaps there is some truth in it.

 

[45crittergitter]

Simple physics - law of inertia: no, it does not continue to accelerate after leaving the barrel.

I think Dan Wesson revolvers have or had gain twist.

 

[Tory]

Not just "race guns"

ANY SVI pistol can be had with the gain-twist rifling of the AET barrel. Heck, my single-stack, iron-sight SVI has one.

 

[Bob R]

I have a Delta down with Ted Yost right now. He is installing a gain twist AET barrel, along with much more work.

He has nothing but praise for the AET barrels when I talk to him. The other Deltas he built using the gain twist rifling shoot "like rifles".

Seems as though the AET barrels are pretty accurate.

bob