Greenhill formula problems (???)

[garrett]

So I just acquired a Remy 700 sps tac in .223 with a 1:9 twist and I have been reading up on bullet "behavior" and when trying to use the greenhill formula to calculate what length of bullet is most acceptable for this twist and velocity and I am coming up with a bullet length of about 1.006" and then some. Which roughly translates to about an 80 grain bullet in .224 diameter. Most people recommend a bullet way below this weight, around mid 60s for a 1:9 twist right? How can I reconcile these two opinions? Or am I just doing the math wrong!

My specs are...

bullet diameter = .224
bullet velocity = 2500 - 2700 (to begin working up)
SG = 10.9 (lead core)
Twist rate = 9.0
"C" = 150 or 180

and bullet length = unknown

any input would be appreciated!

 

[Mordamer]

Re: Greenhill formula problems (???)

You will most likely be able to shoot 75 grain bullets out of that rifle just fine. I have the exact rifle and I shoot Hornady 75 gr. BTHP match bullets 1/2 moa at 100 yards. I could not get the 75 gr. A-max to shoot well. They are a longer bullet. I do not think you will get anything longer than a 75 A-max to stabilize. Try the 70 gr. berger vld bullets. They are nice. Also try the 75 grain bullets from Hornady to see how they do.

 

[garrett]

Re: Greenhill formula problems (???)

All right, will do, thanks Mord

 

[glock24]

Re: Greenhill formula problems (???)

The Greenhill formula is outdated. There are better methods with today's modern bullet designs. One such method is the Miller formula. JBM uses it, and below are the gory details;

http://www.jbmballistics.com/ballistics/bibliography/articles/miller_stability_1.pdf

 

[garrett]

Re: Greenhill formula problems (???)

sweeeeeet, thanks bro. I love this stuff

 

[easternncnative]

Re: Greenhill formula problems (???)

I shoot this rifle also- 77 grain SMKs + 23 grains of Varget is outstanding in mine.

 

[Rich Coyle]

Re: Greenhill formula problems (???)

I fired the 80 grain Sierras in my 9 twist Savage .223 out to 300 yards with no porblem.

 

[garrett]

Re: Greenhill formula problems (???)

good news as well since I have a few in the mail