#1
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20 cal stabiity
How heavy a .20 cal bullet will an 11" twist stabilize? Thinking about a .20 Tactical.
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#2
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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. |
#3
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Most can handle up to the 50 grain mark, with the 1/11 twist.
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#4
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Just an fyi - Bullet length is more important than weight when determining bullet stability.
-BCB
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#5
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Yes. It's a good reference point.
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#6
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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. |
#7
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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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#8
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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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I miss mean Tweets, competence, and $1.79 per gallon gasoline. Yo no creo en santos que orinan. Women and cats will do as they please. Men and dogs should relax and just get used to the idea. Going keyboard postal over something that you read on the internet is like seeing a pile of dog crap on the sidewalk and choosing to step in it rather than stepping around it. If You're Afraid To Offend, You Can't Be Honest - Thomas Paine Last edited by Bayou City Boy; 04-11-2022 at 08:10 PM. |
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