Rifle barrel twist rates

[TehK1w1]

I've seen a bunch of threads recently concerning rifling twist rates, and I was wondering just how tight a twist can be without seriously affecting velocity. I know twist rates can be very slow however, as my 444 Marlin with a 22" barrel has a 1:38" twist is there a twist rate slower than this, or do they just call it a shotgun past that point?

 

[quicktime]

I have heard of a one in fifty twist on round ball muzzle loaders. As for how tight a twist is has to do with bullet weight and construction. Basically you want to spin it just fast enough to stabilize it. So the longer and heavier the bullet is the faster you must spin it to stabilize it. I am sure that some smart guy has a big long math formula to figure it all out. I usually just call the barrel maker and tell him what caliber and what bullet weight I want to shoot and let him figure it out.

 

[RugerOldArmy]

With muzzleloaders, shooting roundballs, too fast a twist rate will hurt accuracy. This depends on the caliber though. I have a few .54 caliber muzzloaders that shoot well with 1-70" and 1-66" twist. 1-48" doesn't work well for .54 (or .50 for that matter), but 1-66" is too slow for .32 or .36 cal roundballs, and 1-48" shoots well.

For centerfire rifles, it seems that it is best to err on the side of the fast twist. But too fast a twist here can cause thin jacket bullets, like varmint bullets, to come apart when they're driven to high velocity. I can do this in a 1-9" .22-250 barrel I have. The shot may be a ten, or an 'X'....or may just end up with a gray puff in the air, not making it to the target.

There is a theoretical ideal for size, based on, I believe it was, Greenhill's (GrenHills?) formula.

 

[Jim Watson]

The .444 is kind of a descendant of the old express rifles, with similarly light short bullets for the caliber and no faster twist than absolutely necessary so as to reduce BP fouling. There might be some slower, but not a lot slower.

One of the experimental fletchette rifles had a 100" twist but that was just to get the sabot to separate, the fletchette was fin stabilized.

Muzzleloaders are different, especially traditional round ball guns.

 

[Don't Tread On Me]

The first time I looked through a 1/7 twist .223 barrel I thought to myself "wow, looks like a corkscrew" ...then I wondered what a bullet went through going through that at 3000fps.

They have 1/6.5 ...

I don't know what the fastest rifle twist available is though. I can't imagine it being much faster. It will cease to be rifling and instead act more like a rasp.

 

[sansone]

as you already know, longer bullets need more stabilizing twist. not so much the weight, LENGTH compared to diameter is the problem. / my recent "poser" is: how come my marlin 22mag w/micro-groove(shallow) rifling is so accurate?

 

[Harley Quinn]

my recent "poser" is: how come my marlin 22mag w/micro-groove(shallow) rifling is so accurate?

Because you are a good shooter