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  #1  
Old 04-10-2022, 05:25 PM
barretcreek barretcreek is offline
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Default 20 cal stabiity

How heavy a .20 cal bullet will an 11" twist stabilize? Thinking about a .20 Tactical.
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  #2  
Old 04-10-2022, 06:15 PM
ken158 ken158 is offline
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If I was building a 20 Tac I would want an 11 twist. My Cooper has a 12 twist and it does very well with 40 grain V-Max and Sierra 39 BK. If I want a heavier bullet, I will just switch up to a .22 cal.

Last edited by ken158; 04-11-2022 at 09:10 PM.
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Old 04-10-2022, 07:45 PM
Bill K Bill K is offline
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Most can handle up to the 50 grain mark, with the 1/11 twist.
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Old 04-10-2022, 09:25 PM
Bayou City Boy Bayou City Boy is offline
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Just an fyi - Bullet length is more important than weight when determining bullet stability.

-BCB
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Old 04-11-2022, 12:20 AM
barretcreek barretcreek is offline
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Quote:
Originally Posted by Bayou City Boy View Post
Just an fyi - Bullet length is more important than weight when determining bullet stability.

-BCB
Yes. It's a good reference point.
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Old 04-11-2022, 12:50 AM
B23 B23 is offline
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Unless it's a short low BC stubby bullet I'd sure think you'd be asking a whole lot from a 11tw at 20 Tactical speeds to stabilize any of the custom 50's, which tend to be higher BC's, bullets. The 50-55's usually benefit from the bigger case capacity cartridges like a 20-250.

Regardless of twist, ballistically speaking at 20Tac speeds, you'll be hard pressed to beat the 39gr Sierra BK's and they just so happen to do very well in 11tw barrels.
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Old 04-11-2022, 09:44 AM
17VLD 17VLD is offline
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Default Sounds like the beginning of a great rifle...

I really think the 11 is perfect for anything up to the 40 grain class of bullet.
Back in the day when all you could get was a 12, I built a 20 BR and had a run on some 500+ yard pd’s out on the Montana border shooting the 39BK and as B23 mentioned they performed very well.I also think the b.c. of the 40 V-Max running .275 is awesome for a 20 cal and will suit you very well, my 20 Duster does great with them.
Matt
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Old 04-11-2022, 06:55 PM
Bayou City Boy Bayou City Boy is offline
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Quote:
Originally Posted by barretcreek View Post
Yes. It's a good reference point.
The length of the spinning gyro (bullet) in relation to its spin rate (barrel twist rate) determines the bullet's stability.

Anyone with swaging tools can make bullets with highly different weights using the exact same jacket length. Both will stabilize in the same barrel. Lengthen the jacket in an otherwise stable bullet and it loses stabiity from the same barrel in flight if it's not spun fast enough.

For example, if you build a stable bullet using a core perhaps 65% the length of the jacket, adding more weight to the bullet as found in a bullet with lead exposed but flush with the open tip (not exposed lead like a spitzer), and that bullet will also be stable in flight in the same barrel. Lengthen the jacket to increase bullet weight and the bullet will become unstable in flight in the same barrel. Exposed lead like found with a spitzer bullet increases both the length of the gyro and adds a bit to the bullet weight.

I've done this with a 38 grain 20 caliber bullet that I swage. I can add more core weight to the same jacket (now weighs ~ 46 grains) and it too will stabilize in the same barrel. Lengthen the jacket or add a spitzer bullet tip and both bullets becomes unstable in the same 11" twist barrel. Yet both bullets with the longer jacket or the spitzer tip shoot great in a faster twist 20-250.

No. I didn't determine that length is the determining factor by citing my example, as that has been known as a fact for years going back to the earliest conical projectiles. But it is easily demonstrated if you swage bullets.

Bullet weight might lead one to believe the jacket is longer but it may not be.

I used the word "gyro" for illustrative purposes to think of a spinning object.

-BCB
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Last edited by Bayou City Boy; 04-11-2022 at 08:10 PM.
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