Barrel twist

Irishtexan
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Joined: Mon Apr 14, 2014 7:30 am

Barrel twist

Post by Irishtexan » Thu Nov 21, 2019 6:06 pm

Im working on a lever gun that will be chambered for a handgun cartridge, while looking at different guns both rifle and handguns i noticed a difference in barrel twists.
For the life of me i dont understand the difference in twist when all the bullets are the same size and weight, can someone shed some light on this for me, dont want the wrong twist on a new barrel, thanks.

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mtngun
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Re: Barrel twist

Post by mtngun » Fri Nov 22, 2019 12:39 pm

Generally best accuracy is obtained with the slowest twist that will reliably stabilize the bullet. That said, in the big scheme of things, the effect of twist on accuracy is small, especially for jacketed bullets, so most hunters and plinkers and gun manufacturers choose a twist that errs on the side of reliable stabilization.

Benchrest shooters, seeking maximum accuracy with a particular bullet weight, tend to choose a twist that is sometimes on the ragged edge of stabilization.

There are various formulas for choosing a twist, none of the formulas are perfect, but the Miller formula is one of the better ones, and the Mountain Molds online design program uses the Miller formula to suggest a sorta minimum twist for a particular bullet.

If you have a particular caliber, particular bullet weight / length, and particular velocity range in mind, then we can throw some twist numbers at it.

Irishtexan
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Joined: Mon Apr 14, 2014 7:30 am

Re: Barrel twist

Post by Irishtexan » Fri Nov 29, 2019 6:33 pm

The bullet will be .400 dia. .765 length, weight will be 240 grains, im not sure of velocity yet, still working on case length.

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mtngun
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Re: Barrel twist

Post by mtngun » Sat Nov 30, 2019 7:33 am

The design program suggests 33" twist for that combination, but I doubt if anyone sells a 33" twist 40 caliber barrel.

Shilen -- only offers 16" twist

Green Mountain -- offers a 48" twist for black powder, a 40" twist for 38-40, and 16" twist for 10mm

Xcaliber -- does not offer a 40 caliber barrel

McGowen -- 40 pistol in 14, 16, 18, 20, 36 inch twists. 40 rifle in 13, 16, 18, 20 inch twists (it's not clear if their 40 rifle is .400")

Hart -- does not offer a 40 caliber barrel

Krieger -- offers a 15" twist barrel (10mm)

Rock Creek -- does not offer a .400 barrel

PacNor -- not taking orders due to a fire

Bartlein -- does not list a .400 barrel

GunPartsCo -- lists a 40" twist for 38-40

Maybe you have a lead on a particular barrel maker, but my quick and dirty search suggests your best bet will be a 20" twist from McGowen. The 40" twist barrels seem iffy with a 240 gr. bullet, but would be fine if you went with a 200 gr..

A 30" twist might be closer to ideal, but no one seems to make one.

Irishtexan
Posts: 17
Joined: Mon Apr 14, 2014 7:30 am

Re: Barrel twist

Post by Irishtexan » Sat Dec 07, 2019 8:53 am

Thanks
Im currently looking at having my barrel rebored and rerifled, but having trouble with someone who can do a .400 bore, also seems like a 6 month wait time on getting it done.

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mtngun
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Re: Barrel twist

Post by mtngun » Sat Dec 07, 2019 10:14 pm

Custom work takes time and money, more so for odd calibers.

Good luck with your project.

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