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  #11  
Old 04-25-2017, 05:55 PM
chuckshooter chuckshooter is offline
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I just did the JM calc and it came back 1.682 for 12t
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  #12  
Old 04-25-2017, 08:11 PM
df06 df06 is offline
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Default 20 cal twist

I shoot two 20VTs, both are 12 twist. I only shoot 32 grain bullets.
Both are very accurate. One is a Kreiger, the other a Shilen.
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  #13  
Old 04-25-2017, 09:32 PM
moorepower moorepower is offline
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1-11 is about perfect for 32-40 grain bullets.
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  #14  
Old 04-25-2017, 09:41 PM
GrocMax GrocMax is offline
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[quote=chuckshooter;254375]
Quote:
Originally Posted by Ratbuster View Post

It's an interesting thought, if the bullet is spinning faster, is it going to cause more aerobatic action on the squirrels that I shoot?
My experience, very much so, until you go too fast and have troubles with jackets disintegrating, or with thin jacket bullets designed for lower velocities.
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  #15  
Old 04-25-2017, 09:45 PM
GrocMax GrocMax is offline
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Quote:
Originally Posted by chuckshooter View Post
I just did the JM calc and it came back 1.682 for 12t
If you enter the correct bullet and tip length for both a 39BK and a 40vmax, then use 0 ft elevation and 4000 ft elevation on a 12t, you see exactly what most of us have seen- 12t can be unstable at sea level in cold dense air but OK at 2500-4000 ft in the summer. 11t is good everywhere.
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  #16  
Old 04-25-2017, 10:42 PM
chuckshooter chuckshooter is offline
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Quote:
Originally Posted by GrocMax View Post
If you enter the correct bullet and tip length for both a 39BK and a 40vmax, then use 0 ft elevation and 4000 ft elevation on a 12t, you see exactly what most of us have seen- 12t can be unstable at sea level in cold dense air but OK at 2500-4000 ft in the summer. 11t is good everywhere.
remember I plan to only shoot 32gr zmax's. I have other guns for 40 gr. 20P, 20tac 204
thanks for the link to JM. I had forgotten about that website. very useful
I am leaning towards 11t, as many have said "good to go everywhere"
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  #17  
Old 04-25-2017, 11:06 PM
GrocMax GrocMax is offline
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204 34g Nosler SHOTS/Midsouth VNE/Midway Dogtowns (same bullet) shoot surprisingly well and splat 'em just fine at a bargain price if you run out of zmax's and are looking for a budget bullet for a 12-13 twist. They have no BC but who cares at short range.
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  #18  
Old 04-25-2017, 11:09 PM
Bill K Bill K is offline
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Default Barrel twist rate for 20ab, 20kb and 20 vt

Quote:
Originally Posted by GrocMax View Post
204 34g Nosler SHOTS/Midsouth VNE/Midway Dogtowns (same bullet) shoot surprisingly well and splat 'em just fine at a bargain price if you run out of zmax's and are looking for a budget bullet for a 12-13 twist. They have no BC but who cares at short range.
I have had good success with the Midsouth VNE all the way too 300-350 yards also in the 20 calibers. Might be short range, too some, but plenty of reach too me. Bill K
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  #19  
Old 04-26-2017, 12:51 AM
Ratbuster Ratbuster is offline
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Default JBM calculator

The JBM calculator is off. Plugging in a Hornady 40 grain at 3800 fps, standard temp and pressure shows a 12 twist as having a 2.513 SG. Not hardly.

The Berger calculator says SG of .841 at sea level and .981 at 4200 feet for the same bullet with 12 twist. The Berger result is closer to what you would expect based on results 20 cal shooters get; there are many 20 cal owners with 12 twists that can not get the 40 grain Hornady stabilized.

Just for fun I plugged in a 16 twist in the JBM calculator and it showed a SG of 1.413. I don't think so.
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  #20  
Old 04-26-2017, 12:55 AM
chuckshooter chuckshooter is offline
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Quote:
Originally Posted by Ratbuster View Post
The JBM calculator is off. Plugging in a Hornady 40 grain at 3800 fps, standard temp and pressure shows a 12 twist as having a 2.513 SG. Not hardly.

The Berger calculator says SG of .841 at sea level and .981 at 4200 feet for the same bullet with 12 twist. The Berger result is closer to what you would expect based on results 20 cal shooters get; there are many 20 cal owners with 12 twists that can not get the 40 grain Hornady stabilized.

Just for fun I plugged in a 16 twist in the JBM calculator and it showed a SG of 1.413. I don't think so.
check your numbers, that's not what I get
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