Variable twist rate ?

[Stob]

None of the top barrel makers sell cheap barrels anymore. $300 plus is the norm now days. Most of the barrels Grizzly sells are focused around the high power shooters, 30" barrels are 30 to 40 more than a standard blank. And every barrel maker is swamped with orders. Kreiger and Bartlein are in the biggest demand.

 

[ricsmall]

Yes, quite a wait for a bartlein tube. I waited 8 months for one chambered in 6.5 Grendel. Most of that time was waiting for the barrel, then the gunsmith working thru the backlog. They're worth it. That gun will shoot sub Moa out to 730 yards and its an ar15. Plan to take it further this spring. Thinking of using the same barrel and chamber on a bolt gun project.

Richard

 

[JPigg55]

Thanks everyone, I'd never heard of a "Gain Twist" barrel before.
I'll have to see if there are any videos or info on how they do it. On the surface, wouldn't seem to be an easy process.

 

[cdhknives]

Gain twist is popular among some cast bullet shooters too. It reduces thrust on the rifling/bullet during the biggest part of the acceleration, then spins up the bullet at the end of the barrel.

Recovered bullets have strange looking rifling marks too.

 

[paperpuncher]

The modern method of manufacturing a gain twist barrel is with a purpose built programmable CNC rifling machine.
Your friend may have a 1 in 14 down to a 1 in 5 twist. I have never seen one that is that radical. I would like to see a recovered bullet that has been fired in a barrel of that spec, it would have to be pretty smeared and deformed by the rifling. I wonder what the application would be for a 1 in 5 twist in a .223 The heaviest bullet generally available is a 90 grain, and it will stabilize with a 1 in 7. Subsonic maybe?
Usually the reduction is 1/2 to 1 1/2 turns, say from 1 in 12 to 1 in 11.25 in a .308. I have used gain twist barrels and they can work very well with the correct combination of bullet and twist reduction.

 

[Stob]

The jury is still out whether a gain will shoot better than a normal twist barrel in the benchrest community. A good barrel is where you find one, regardless of who made it, how many grooves it has, etc. Some have done very well with them, but many Bartleins have done well.

A typical barrel will take some work to find the sweet spot that makes it shot the best, then the shooter has to learn how to keep that sweet spot as it wears, weather changes, etc.

Then there are the "hummer"barrels. You'll know when you get one. They just keep shooting, they shoot through conditions, they forgive many things, don't need the tweaking all the time.

I've had two, and have seen middle of the road shooters have an exceptional year until the barrel wears out. Then it's back to normal. I know many don't get into the extreme accuracy thing, but there are differences in barrels.

 

[JPigg55]

I or he may have been mistaken on the numbers. I was just more interested in learning about it, I just never knew it existed.

 

[Stob]

I remember reading years ago that this was used in artillery barrels. As I recall the Germans utilized this in the huge cannons and rail guns. Not sure the source of this as it's coming from memory.

I believe you are correct with this. The artillery shells would strip the rifling out of the first portion of the barrel trying to get the heavy projectile to spin. So they started out slow and increased down the barrel, it must have worked.

Brownells used to sell gain twist barrels long ago, so it's not new to small firearms.

 

[Garryzgarage]

I have only seen this in big bore guns like the 155, but never as radical as what your saying, also in the days of my shooting black powder 50 and 64 cal. Rifle, they had a gain twisted, Green River Gunworks built gain twist barrels, this is my quarters worth, Garry