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Old 09-16-2011, 09:18 AM   #1
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Default Rifling Twist Ratio and it's Significance?

Just what the title says. We all know what rifling is and what it does, but how does the difference in one manufacturers twist ratio help or hurt their firearms performance?

Example:
Glock 27, right hand twist at 1 : 9.48in.

Ruger LC9, right hand twist at 1 : 10in.

The ratio seems to be mostly consistent within any given manufacturer, but whats the real difference here? I am assuming that a tighter twist will grip the bullet harder, causing the bullet to take longer to exit while also allowing for greater powder burn time...? I guess its not really all that important, but I just gotta know!

Thanks!



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Old 09-16-2011, 10:19 AM   #2
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I don't know but that's a good question and I am waiting to learn the answer, too.



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Old 09-16-2011, 10:38 AM   #3
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Quote:
Originally Posted by BigByrd47119 View Post
Just what the title says. We all know what rifling is and what it does, but how does the difference in one manufacturers twist ratio help or hurt their firearms performance?

Example:
Glock 27, right hand twist at 1 : 9.48in.

Ruger LC9, right hand twist at 1 : 10in.

The ratio seems to be mostly consistent within any given manufacturer, but whats the real difference here? I am assuming that a tighter twist will grip the bullet harder, causing the bullet to take longer to exit while also allowing for greater powder burn time...? I guess its not really all that important, but I just gotta know!

Thanks!
Here is a good discussion of barrel twist rate from the AR15 section. The basic principles are universal. In the example above the bullet is spinning slightly faster when it exits the barrel of the G27 compared to the LC9. Although in this example the difference is negligible.


http://www.firearmstalk.com/forums/f20/understanding-barrel-twist-bullet-weights-44557/

Heavier (longer) bullets require more "spin" to stabilize them while in flight.
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Old 09-16-2011, 10:54 AM   #4
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As said- the "faster" the twist (it is the number of linear inches of barrel to make one complete turn) the faster the bullet is spun. Some of my muzzleloaders have EXTREMELY slow rates of twist- like 1 in 64. While we tend to think in terns of heavy and light bullets, it is actually the LENGTH of the bullet that governs the need for twist- but longer bullets tend to be heavier than short bullets (all other things being equal)

Rate of twist does not govern the LINEAR speed of the bullet, but the ROTATIONAL speed.

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Old 09-16-2011, 11:52 AM   #5
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Thanks for clearing this up for me. I was baffled that (from what I could see) no one had ever asked this question before! Nor did an explanation exist.

Once again, thanks!



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