TWIST, VELOCITY, AND STABILITY

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  • Last Post 30 January 2019
joeb33050 posted this 26 January 2019

 

TWIST, VELOCITY, AND STABILITY

 As velocity falls, eventually bullets become unstable.

 The barrel tested here was originally a Stevens 223 Rem, re-chambered to 22-250 by Ken Campbell. I sawed it off to 16.5” and chamfered the muzzle.

 

Titegroup powder, misc. primers.

 

5-shot 100 YARD GROUP” is the average of all groups with that load.

 

The 40 and 53 grain Nosler bullets have plastic tips ~.1” long. Greenhill twist is calculated with and without the tips.

 

MV is measured with a chronograph; 100 YARD V is calculated using the published BC.

 

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joeb33050 posted this 26 January 2019

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  • Liked by
  • RicinYakima
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joeb33050 posted this 26 January 2019

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joeb33050 posted this 27 January 2019

 

 

 

The Greenhill twist for the 40 and 53 grain bullets is slower than the barrel twist. For the 68 grain bullets, the Greenhill twist, 7.7”, is faster than the 9” barrel twist. The bullets are tipping, but the groups are at least reasonable to ~1200 fps 100 yard velocity.

 

Note that all three bullets start shooting wild at about the speed of sound at 100 yards.

 

Next is a 223 REM Iffland barrel. At my test velocities, the 68 grain bullet did not stabilize.

 

 

 

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joeb33050 posted this 27 January 2019

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joeb33050 posted this 27 January 2019

Attached Files

joeb33050 posted this 27 January 2019

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joeb33050 posted this 27 January 2019

 

My maximum charge of Titegroup with 53 grain bullets is 8.5 grains. To get a notion of accuracy above 2350 fps MV, charges of 10 to 12 grains of Blue Dot were tested, as shown.

 

Note that the 40 grain bullet becomes wild around the speed of sound; and the 53 grain bullet in the slow twist, 14” barrel, gets wild around 1900 fps at 100 yards.

 

 

 

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Ken Campbell Iowa posted this 29 January 2019

joeb::  this is most interesting, but very perplexing ....   

i am still working on my questions ...

*********

this is like my brother-in-law, who found that no matter what kind of booze he chased with spring water , he kept getting buzzed up ....  the culprit was obviously the spring water ....

*****************

so blue dot makes bullets tumble ?? ....  help me out here ....

since i am always thinking that mysterious results will give us the most important information, this should be a gold mine ... 

thank you for your enormous and continuing efforts .

ken

 

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joeb33050 posted this 30 January 2019

joeb::  this is most interesting, but very perplexing ....   

i am still working on my questions ...

*********

this is like my brother-in-law, who found that no matter what kind of booze he chased with spring water , he kept getting buzzed up ....  the culprit was obviously the spring water ....

*****************

so blue dot makes bullets tumble ?? ....  help me out here ....

No. I'm testing to see what happens as V is reduced. The 14" twist bbl 53 gr bullet started being very inaccurate at 8.5 titegroup, my max load. To see accuracy at higher V, went to Blue Dot.

 

since i am always thinking that mysterious results will give us the most important information, this should be a gold mine ... 

thank you for your enormous and continuing efforts .

ken

 

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