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greenhill formula |
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pyro6999
Optics Retard OT TITAN Joined: December/22/2006 Location: North Dakota Status: Offline Points: 22034 |
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Posted: April/13/2008 at 11:14 |
so i started playing with this today and in the original format 150*diamtersq/length i figured out that the constant(150) really didnt work so well, they mentioned using 180 instead which works better, anybody else use this? i see it can be quite helpful in determining the proper bullet weight for your rifle based on its twist.
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They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead" 343 we will never forget God Bless Chris Ledoux "good ride cowboy" |
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tahqua
MODERATOR Have You Driven A Ford Lately? Joined: March/27/2006 Location: Michigan, USA Status: Offline Points: 9042 |
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I have Greenhill's Formula set up in an Excel file and use it all the time.
When using this formula I have found that some manufacturers are rifling their barrels for the light for caliber screamer crowd. I sure don't want to get going on that one, now. |
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pyro6999
Optics Retard OT TITAN Joined: December/22/2006 Location: North Dakota Status: Offline Points: 22034 |
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is there any way you can send me that doug??
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They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead" 343 we will never forget God Bless Chris Ledoux "good ride cowboy" |
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tahqua
MODERATOR Have You Driven A Ford Lately? Joined: March/27/2006 Location: Michigan, USA Status: Offline Points: 9042 |
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I'll email it, pronto.
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Dale Clifford
Optics Jedi Knight Joined: July/04/2004 Location: United States Status: Offline Points: 5087 |
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here is another although not greenhill will run directly in matlab
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Dogger
Optics Jedi Master Joined: January/02/2007 Location: Ontario, Canada Status: Offline Points: 8902 |
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150's generally ok up to 2800fps. use 180 over 2800.
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God save the Empire!
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300S&W
Optics God Joined: January/27/2008 Location: Burlington,WV Status: Offline Points: 10592 |
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The 150 up to 2800 worked for me when trying to figure out the twist to go with for a 9.3x62. Couldn't decide if 1-12 or 1-14 was best. The Greenhill formula worked out to 1-13.something(can,t recall) so I decided on 1-12. Should work for all bullet weights.
til later
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pyro6999
Optics Retard OT TITAN Joined: December/22/2006 Location: North Dakota Status: Offline Points: 22034 |
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ive been running this on some of my bullets and the numbers arent adding up for some reason
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They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead" 343 we will never forget God Bless Chris Ledoux "good ride cowboy" |
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tahqua
MODERATOR Have You Driven A Ford Lately? Joined: March/27/2006 Location: Michigan, USA Status: Offline Points: 9042 |
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I don't have my flash drive with me. Let me know what bullets and caliber you are running and I'll take screen shots for you. I'll then posst them here. It definitely works and is Greenhills to a T.
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pyro6999
Optics Retard OT TITAN Joined: December/22/2006 Location: North Dakota Status: Offline Points: 22034 |
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what im saying is that according to the program i aint shooting the right weights in my rifle
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They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead" 343 we will never forget God Bless Chris Ledoux "good ride cowboy" |
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tahqua
MODERATOR Have You Driven A Ford Lately? Joined: March/27/2006 Location: Michigan, USA Status: Offline Points: 9042 |
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The heavier the bullet the faster the twist, in general terms. Greenhill's proves this out.
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pyro6999
Optics Retard OT TITAN Joined: December/22/2006 Location: North Dakota Status: Offline Points: 22034 |
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my twists arent agreeing with my bullet choices, but my accuracy is pretty good
here is the fun part when i use the 180*d^2/L it gets worse Edited by pyro6999 - April/14/2008 at 20:51 |
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They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead" 343 we will never forget God Bless Chris Ledoux "good ride cowboy" |
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tahqua
MODERATOR Have You Driven A Ford Lately? Joined: March/27/2006 Location: Michigan, USA Status: Offline Points: 9042 |
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This may be true, especially when using boat tails. The formula takes into account bullet length but not the center of gravity for the projectile. It is a generalization, but it does come reasonably close.
Play with some numbers for the 5.56 for example. Run the 55gr., 62gr., 69gr and 75 gr weights. I think you will see a correlation with the common twist rates in the AR-15 market. The heavy bullets need a 1/7", the 1/9" is a compromise. Edited by tahqua - April/14/2008 at 21:31 |
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pyro6999
Optics Retard OT TITAN Joined: December/22/2006 Location: North Dakota Status: Offline Points: 22034 |
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ok i ran it again and my .280 is off as is my .264 win my 6.5 is pretty close my 22-250 is dead on with the 180*d^2/l
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They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead" 343 we will never forget God Bless Chris Ledoux "good ride cowboy" |
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