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# Barrel rifling and handguns

Discussion in 'General Glocking' started by flw, Nov 14, 2012.

1. ### flw

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In handguns only, what are the effects of different twist rates, barrel lenght and bullet weights? Left vs right?

Specifically 9mm 115 gr. on up to 148 gr. and the same thing for other common handgun calibers.(40 S&W, 45ACP, 10mm)

This is for handgun calibers only. Thank You.

2. ### nraman

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The 9mm Glocks use a 1x9.84" twist which is on the fast side and guarantees stabilization of all common weights of bullets.
The heavier (actually it is the length that matters) bullet needs faster twist.

3. ### M 7

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Left and right twists matter very little, if at all.

Heavier (that is, longer) bullets require a faster rate of spin in order to stabilize them during flight through air than lighter (shorter) bullets do.

A relatively simple and useful formula for determining the minimum required rate of twist (expressed in as one complete revolution in a certain number of inches) is the Greenhill formula--

150 x (D²) ÷ L = distance the bullet must travel to make one complete revolution (in inches)

where D is the bullet's diameter in decimal inches and L is its length (also in inches).

Last edited: Nov 14, 2012
4. ### gumpmonkey

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Am I understanding this correctly? A lighter shorter bullet
will be more stable , i.e. more accurate , than a longer heavier one at any given rate of twist. - Jp

5. ### rdstrain49

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Nope, that's not what he said.

6. ### rimshaker

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Generally the faster the twist rate, the better. Especially for heavier bullets.

Twist direction (LH, RH) not so important unless you're using a silencer. The force generated in the twist direction usually helps prevent the can from loosening while shooting (depending on which thread mount you have).

7. ### Bruce M

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I thought you wanted a left hand twist if you were north of the equator and a right hand twist south of the equator.

8. ### M 7

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Nearly so.

Yes, once stabilized, a lighter (and therefore shorter) bullet will be better stabilized than a heavier (longer) bullet subjected to an identical rate of spin. There is the issue of overstabilization (imparting a much higher rate of spin than is necessary to achieve stability), but like anything else, done to excess, it creates problems of its own. Overdone, it can result in degraded flight characteristics (waaaay too fast can cause the bullet to disintegrate immediately after leaving the muzzle) and may cause delayed yaw cycle and upset in denser mediums like flesh, effecting the amount of damage done to a target.

Accuracy, is a function of more than just a bullet's gyroscopic stabilization- its construction, shape, and material uniformity, air density, pressure, humidity, temperature and many other factors are also very important. While it is an important factor, it is not the only one in determining the accuracy of a bullet.

9. ### M 7

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Coriolis effect?

Yeah, it matters, but it is only significant in really large scale frames of reference like artillery that reaches for miles or dozens of miles and more.

I wish that I was so accurate that it mattered for me, but alas, I am but a mere mortal who is elated if he can turn in a 1 MOA 3 shot group at 300 yards.

Last edited: Nov 15, 2012
10. ### JW1178

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What if you fire it while on a treadmill?

11. ### rdstrain49

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You won't get anywhere

12. ### M 7

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You'll shoot your eye out, kid.

Last edited: Nov 15, 2012