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Very Hot Topic (More than 25 Replies) 16" twist in 32/40 (Read 3927 times)
Dellet
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Re: 16" twist in 32/40
Reply #15 - Feb 3rd, 2023 at 3:16am
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JLouis wrote on Feb 1st, 2023 at 6:16pm:
For a 16 twist it would be three times the groove diameter for the bullets length. 
Weight is actually not the determining factor.

I’m curious about this formula. What are the factors that determine 3x groove?

What would be the multiplier for a 14 or 18 twist?
Is it the same for all bore sizes?
  
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JLouis
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Re: 16" twist in 32/40
Reply #16 - Feb 3rd, 2023 at 7:35am
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Dellet that was handed down to me by Barry Darr for use in 16 twist and it would not true for others.
  

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Cbashooter
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Re: 16" twist in 32/40
Reply #17 - Feb 3rd, 2023 at 8:07am
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Dellet wrote on Feb 3rd, 2023 at 3:16am:
JLouis wrote on Feb 1st, 2023 at 6:16pm:
For a 16 twist it would be three times the groove diameter for the bullets length. 
Weight is actually not the determining factor.

I’m curious about this formula. What are the factors that determine 3x groove?

What would be the multiplier for a 14 or 18 twist?
Is it the same for all bore sizes?


x3.5 for the 14 twist
x2.7 for the 18

best I can tell its based on Greenhill data 


  
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gnoahhh
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Re: 16" twist in 32/40
Reply #18 - Feb 3rd, 2023 at 9:48am
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[quote

x3.5 for the 14 twist
x2.7 for the 18

best I can tell its based on Greenhill data 


[/quote]

And that's fine, I think, for our low vel cast bullets. But, as with all such ballistic formulas there are caveats. Velocity is a big one - faster allows for the stabilization of a bullet that may not be perfectly ideal for the rate of twist. Air density - what works at higher altitude may not at sea level (I've encountered that phenomenon living here on the shores of the Chesapeake Bay). Air temperature is a factor also. Therein lies why one encounters little mysteries that don't fit twist rate formulas.
  
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JLouis
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Re: 16" twist in 32/40
Reply #19 - Feb 3rd, 2023 at 10:18am
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When I was still making bullet moulds for something other than a 16 twist.
I typically used the same lengths and designs that were already proven to be very competitive for Schuetzen benchrest.   
I accumulated quite a collection just for this type of use.
  

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calledflyer
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Re: 16" twist in 32/40
Reply #20 - Feb 3rd, 2023 at 11:48am
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JLouis wrote on Feb 3rd, 2023 at 10:18am:
I typically used the same lengths and designs that were already proven to be very competitive for Schuetzen benchrest.  
I accumulated quite a collection just for this type of use.



so, you were just using somebody's empirical evidence to copy the work. 
For a moment it sounded like you were an inovator
  
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JLouis
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Re: 16" twist in 32/40
Reply #21 - Feb 3rd, 2023 at 12:28pm
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I was innovative and I did make some cherries of my own design to try. 
If any proved to be worth while I would also cut a mould for my friends if they were interested in trying it.
I was not in the business of making moulds to sell, I only did it for friends and they were typically also at no charge to them. 
More times than not if I re-barreled a rifle for them and to something different than it originally was I would also cut a mould for them. 
I would also bore out a baseband if the need arised. 
Did one for Marlinguy way back when and also a friend and I believe it was from .321 or .322 to .324 and he could probably recall it now better than I can. 
I also have 36 Darr bullet cherries that were also gifted to me from 22 to 40 of various designs that I could also use.
« Last Edit: Feb 3rd, 2023 at 12:36pm by JLouis »  

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Re: 16" twist in 32/40
Reply #22 - Feb 3rd, 2023 at 1:21pm
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This is a Cherrie that I was making that I wanted to try in my 28-35. 
I had been wanting to try a spitzer with a 7 diameter ogive / 7 times the bullets diameter. 
It is now to the shape that I want and I still need to cut the flutes.
Then to harden it, sharpen it with a back bevel so the trailing edges do not make any contact, while also not changing the bullets diameter. 
It was just pretty much a hobby for me and for also being able to help out my friends if in need. 
Probably cut close to 50 moulds off the top of my head and I now don't even have one of own. 
Pretty much just gave them all away and to the point that I had to actually make one for myself to use for a match. 
Cutting a mould is easy and it is in the making of the mould block blanks that is kind of a pain in the A--s and also very time consuming as well.   

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Re: 16" twist in 32/40
Reply #23 - Feb 3rd, 2023 at 1:21pm
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gnoahhh wrote on Feb 3rd, 2023 at 9:48am:
[quote

x3.5 for the 14 twist
x2.7 for the 18

best I can tell its based on Greenhill data 




And that's fine, I think, for our low vel cast bullets. But, as with all such ballistic formulas there are caveats. Velocity is a big one - faster allows for the stabilization of a bullet that may not be perfectly ideal for the rate of twist. Air density - what works at higher altitude may not at sea level (I've encountered that phenomenon living here on the shores of the Chesapeake Bay). Air temperature is a factor also. Therein lies why one encounters little mysteries that don't fit twist rate formulas. [/quote]

I  agree with that fully .I've got a couple of Spitzer bullets that are technically too long for the velocities that I am shooting in 22 caliber and the twist rates. Couple people have run them on quick load and tell me I'm full of s***. I don't know why it works in my situation but you have to shoot something to figure it out rather than come up with theories.and scare yourself out of trying something new
  
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Re: 16" twist in 32/40
Reply #24 - Feb 3rd, 2023 at 1:51pm
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I personally do not believe that the Greenhill Formula actually works for our breech seating needs. 
CBA Shooter I do agree with you a rifle with the same length barrel and the same twist. 
Including the velocities being real close to being the same, one will shoot extremely well and the other possibly not. 
I built three identical breech seating 25-35's with the same barrel contour, maker  and length.
All also being chambered the same with zero headspace but no three exactly liked he same things. 
Bullet was the same and the Mos 120 grain spitzer the difference was in the primers, powder and possibly the breech seating depth.

  

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Re: 16" twist in 32/40
Reply #25 - Feb 3rd, 2023 at 3:51pm
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I sometimes shoot -32-40 with black powder.  Lower velocity than a typical smokeless load I think.  I get a lot less tipping with slightly longer semi-spitzers than with blunt nosed bullets, particularly in cold weather.   

Chris.
  
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JLouis
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Re: 16" twist in 32/40
Reply #26 - Feb 3rd, 2023 at 5:02pm
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Based on my own personal experience a spitzer bullet can be about 30 thousandths longer than a flat or a round nose bullet at times.  
Pretty much depends on the center of gravity and also the center of pressure but I have also not yet ran into that specific issue yet.
« Last Edit: Feb 3rd, 2023 at 5:26pm by JLouis »  

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Re: 16" twist in 32/40
Reply #27 - Feb 3rd, 2023 at 5:18pm
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The more inputs of bullet shape and weight used to calculate stability, the more accurate the prediction will be. 

Bullet shape does matter.

It gets worse with lube grooves because they change the balance of the bullet.

Most calculators out there don’t even know which end of the bullet is loaded forward, it’s no wonder there are huge discrepancies in what will or won’t work.

Never mind distance to target. 

I generally use a drag or form calculator because they allow inputting  the bullet shape and weight and generate a relative number for comparing just how stable the bullet is.

More often than not I use it after shooting and confirming if the bullet is stable. This has given me a much better idea of the reliability of a chosen calculator.
  
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Re: 16" twist in 32/40
Reply #28 - Feb 3rd, 2023 at 7:56pm
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Dellet wrote on Feb 3rd, 2023 at 5:18pm:
The more inputs of bullet shape and weight used to calculate stability, the more accurate the prediction will be. 

Bullet shape does matter.

It gets worse with lube grooves because they change the balance of the bullet.

Most calculators out there don’t even know which end of the bullet is loaded forward, it’s no wonder there are huge discrepancies in what will or won’t work.

Never mind distance to target. 

I generally use a drag or form calculator because they allow inputting  the bullet shape and weight and generate a relative number for comparing just how stable the bullet is.

More often than not I use it after shooting and confirming if the bullet is stable. This has given me a much better idea of the reliability of a chosen calculator.

  There it is gentlemen, "in a nutshell".    
« Last Edit: Feb 4th, 2023 at 7:46am by Jeff_Schultz »  

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Re: 16" twist in 32/40
Reply #29 - Feb 3rd, 2023 at 9:01pm
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Not really and it actually all does boil down to the actual time of flight. 



  

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