Choosing a bullet with the Greenhill formula

[bullfisher]

Has anyone successfully chosen a bullet this way?
Its a formula used to find the optimum bullet length (weight) for your barrel's twist rate.
Mr. Greenhill was a military academy instructor from 1876 to 1906. He discovered that the optimum twist rate for a bullet could be determined by dividing 150 by the bullets length in calipers. shape and design of the bullet shows less of an effect in velocities under 2500fps. Velocities over 2500 was best to err on a reduced twist, but more recent studies of the formula showed to err on the slightly faster side of twist.
Example: .223 a 55grn fmj. is .647 long. the dia. is .224 and dividing 224 into 647= 2.89 calipers long. Dividing 2.89 into 150= 51.90 or an ideal twist rate of one turn in 51.90 calipers. And multiplying 51.90 by the .224 number= one turn in 11.63" for this particular bullet. If you use the 70 grn fmj you get .785 long and the formula yields a 9.60 twist rate, so a 1:9 or 1:10 would be considered optimum.
My 300wsm in 1:10 shows an optimum 180grn. But you pro 1000+ shooters (something I'm trying to achieve) are shooting 300wm with 200+ grn bullets. Is the Greenhill formula worthless for this aplication?

 

[Temp9]

Re: Choosing a bullet with the Greenhill formula

Greenhill's formula is extremely outdated and not suitable for modern bullets. The formula was developed for lead, round nose, flatbase bullets. The modern version of this formula would be the Miller twist rule. Unlike the Greenhill formula, the Miller twist rule accounts for modern bullet shapes, velocity, atmospheric conditions, etc. Google for more info and check out JBM's stability calculator using this formula.

 

[YAOG]

Re: Choosing a bullet with the Greenhill formula

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Temp9</div><div class="ubbcode-body">Greenhill's formula is extremely outdated and not suitable for modern bullets. The formula was developed for lead, round nose, flatbase bullets. The modern version of this formula would be the Miller twist rule. Unlike the Greenhill formula, the Miller twist rule accounts for modern bullet shapes, velocity, atmospheric conditions, etc. Google for more info and check out JBM's stability calculator using this formula. </div></div>

^^^^
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This!

 

[bullfisher]

Re: Choosing a bullet with the Greenhill formula

The jbm calc is pretty simple and shows me close with 180 and 220 grn. I guess its a shoot and see. Thanks!

 

[Cacciatore]

Re: Choosing a bullet with the Greenhill formula

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bullfisher</div><div class="ubbcode-body">The jbm calc is pretty simple and shows me close with 180 and 220 grn. I guess its a <span style="font-weight: bold"><span style="text-decoration: underline">shoot and see</span></span>. Thanks! </div></div>

Haha. Like the targets.