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***WARNING*** This Read requires a Brain (Brian)

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Forum Name: Reloading & Ballistics
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Topic: ***WARNING*** This Read requires a Brain (Brian)
Posted By: 338LAPUASLAP
Subject: ***WARNING*** This Read requires a Brain (Brian)
Date Posted: October/13/2011 at 19:59
This post is a great read even if not a .338LM or .338 Shooter.

Alfred George Greenhill

In 1879, Greenhill developed a http://en.wikipedia.org/wiki/Rule_of_thumb - - twist rate for lead-core bullets. This shortcut uses the bullet's length, needing no allowances for weight or nose shape. http://en.wikipedia.org/wiki/Alfred_George_Greenhill#cite_note-2 - - [3] Greenhill applied this theory to account for the steadiness of flight conferred upon an elongated projectile by http://en.wikipedia.org/wiki/Rifling -

where:

  • C = 150 (use 180 for muzzle velocities higher than 2,800 f/s)
  • D = bullet's diameter in inches
  • L = bullet's length in inches
  • SG = bullet's http://en.wikipedia.org/wiki/Specific_gravity -



Replies:
Posted By: 338LAPUASLAP
Date Posted: October/13/2011 at 20:11
I was trying to be ironic not rude sorry about those who are scratching their heads wondering if they should read this post...

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No one


Posted By: 338LAPUASLAP
Date Posted: October/13/2011 at 20:15
For those readers that do not know Brian he is probably the best Ballistician of the 21st century.

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No one


Posted By: trigger29
Date Posted: October/13/2011 at 20:27
While a good read, the greenhill formula is a bit dated. You may want to try the miller stability formula too. They actually have a calculator for it on JBM's site. I've found it to predict needed twist rate with what I'd expect from my real world results.
 
Here's a link. http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi - http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi


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"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."


Posted By: 338LAPUASLAP
Date Posted: October/13/2011 at 20:35
I know, I use some other stuff I was actually just trying to get people that don't know hooked...
 
Funny part of the whole thing is Brian Litz asking Johnny from the Streets why???


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No one


Posted By: trigger29
Date Posted: October/13/2011 at 21:01
I'm guessing because what they are doing doesn't make sense to him. My bullets that Brandon shot out of his .338 RUM are much longer than Berger's 300 gr, and he shot them from a 1-10" twist with no trouble. I think he's making a point, or wondering why these guys see the need to go tighter. But that's just my best guess. I really have no idea why he'd ask such a question. I'm guessing if anyone would know the answer, he should.

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"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."


Posted By: 338LAPUASLAP
Date Posted: October/13/2011 at 21:09
Exactly, that is why.
 
Have you had a chance to read his books? 


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No one


Posted By: trigger29
Date Posted: October/13/2011 at 21:14
I have not. I probably should. Just too many things to spend money on right now, and I guess I haven't made that a priority. It's on the list though.

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"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."


Posted By: Bigdaddy0381
Date Posted: October/14/2011 at 07:14
Originally posted by 338LAPUASLAP 338LAPUASLAP wrote:

Exactly, that is why.
 
Have you had a chance to read his books? 
 
I have read the second edition a few times. It takes me a little longer to take in what I read, rather than real world of "just doing it". I have also noticed you can have the perfect surface bearing and twist rate but if the agive and base is angled to much or not enough the bullet still will not fly like it should. Also you can cheat the twist rate "sometimes", but it depends on the load and rifle and is not a normal thing.


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P&Z Firearms , Pro gun cleanings and gun repair and wood refinishing.

Ecclesiastes 10:2



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