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Double Rifles, Single Shots & Combinations >> Double Rifles

mhb
.275 member

Reged: 20/09/05
Posts: 77
Loc: S.E. Arizona

Re: Twist? An easy question.
17/12/05 10:20 AM

The rate of twist (rifling pitch) needed to stabilize a given bullet depends on its length (if of conventional materials), and to some extent, shape, as well as velocity, though to a lesser extent. The basic rule is that you should use a pitch rate which will stabilize the longest (and usually, heaviest) bullet you intend to use in a given caliber, since understabilized bullets (spun at too low RPM) will not maintain the proper point-first attitude and are wildly inaccurate, while overstabilized bullets (spun faster than absolutely necessary to stabilize them) do not suffer from inaccuracy to any real extent. Usually a pitch rate is chosen to give a stability factor of 1.2 or greater (that is, 1.2 times the theoretical RPM necessary for bullet stabilization) - this helps compensate for bullets which are not 'perfect' in any way (usually having the center of mass off the center of rotation due to imperfect shape or a jacket and core not perfectly concentric with each other).
There are several formulae used to calculate the theoretical pitch needed for a given bullet - the Greenhill is a good one for most common sporting uses.

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Edited by mhb (17/12/05 10:27 AM)

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Subject	Posted by	Posted on
Twist? An easy question.	bulldog563	17/12/05 09:21 AM
Re: Twist? An easy question.	500Nitro	17/12/05 09:37 AM
Re: Twist? An easy question.	bulldog563	17/12/05 09:41 AM
Re: Twist? An easy question.	mhb	17/12/05 10:20 AM
Re: Twist? An easy question.	500Nitro	17/12/05 11:19 AM
Re: Twist? An easy question.	Marrakai	17/12/05 11:34 AM
Re: Twist? An easy question.	mhb	18/12/05 03:41 AM
Re: Twist? An easy question.	Marrakai	18/12/05 10:58 AM
Re: Twist? An easy question.	mhb	19/12/05 04:04 AM
Re: Twist? An easy question.	Marrakai	19/12/05 10:20 AM
Re: Twist? An easy question.	mhb	19/12/05 11:42 AM
Re: Twist? An easy question.	Marrakai	19/12/05 04:26 PM
Re: Twist? An easy question.	mhb	20/12/05 01:52 AM
Re: Twist? An easy question.	Marrakai	20/12/05 02:01 PM
Re: Twist? An easy question.	mhb	21/12/05 02:18 AM
Re: Twist? An easy question.	CorditeBlues	21/12/05 01:15 AM
Re: Twist? An easy question -- Maybe	CorditeBlues	21/12/05 01:21 AM
Re: Twist? An easy question -- Maybe	mhb	21/12/05 02:25 AM
Re: Twist? An easy question -- Maybe	Marrakai	21/12/05 01:39 PM
Re: Twist? An easy question -- Maybe	mhb	22/12/05 02:50 PM
Re: Twist? An easy question -- Maybe	Marrakai	22/12/05 11:41 PM
Re: Twist? An easy question -- Maybe	mhb	23/12/05 01:41 AM
Re: Twist? An easy question -- Maybe	Marrakai	23/12/05 11:41 AM
Re: Twist? An easy question -- Maybe	500grains	23/12/05 02:19 PM
Re: Twist? An easy question -- Maybe	Marrakai	24/12/05 11:43 AM
Re: Twist? An easy question -- Maybe	mhb	25/12/05 01:07 AM
Re: Twist? An easy question -- Maybe	mhb	24/12/05 01:49 AM
Re: Twist? An easy question -- Maybe	bulldog563	23/12/05 02:43 PM
Re: Twist? An easy question -- Maybe	500grains	22/12/05 05:13 PM
Re: Twist? An easy question -- Maybe	DUGABOY1	22/12/05 05:09 AM
Re: Twist? An easy question -- Maybe	homemadeDR	22/12/05 06:21 AM
Re: Twist? An easy question.	500Nitro	17/12/05 10:09 AM

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