Greenhill Formula for selecting projectile length....question about value of this formula & how to best choose a specific projectile for paper target.

[want2learn]

i was reading a long range rifle text and they mentioned the Greenhill Formula as one way of selecting a projectile. The formula is ((bullet diameter) x (bullet diameter)) x 150 / rate of twist.

For example for my 6.5x47L with a 1:8 rifle twist that would be:
0 .264 x 0.264 = .069696
.069696 x 150 = 10.4544
10.4544/8 = 1.30 inch

When i look at the Lapua projectile site data i find that both their 123gn and the 144gn projectiles have a length of 1.3 inch
i never hear anyone discussing use of 144gn projectiles in the 6.5x47L

Wondering why that is? Has this formula not proven well in practice? For shooting paper targets, Is there a better way to choose projectiles in addition to BC? thank you

 

[918v]

Use Berger’s sg calculator. It is better for modern jacketed projectiles.

 

[want2learn]

thank you for that reference...

i just did some preliminary calculations and it seems i should have chosen a 7.5 twist rate barrel and 120gn projectiles as that combination would have yielded the highest SG.

i've got so much to learn

 

[918v]

You don’t need the highest sg. Just the sg to make the bullet stable.

 

[want2learn]

interesting.....need to learn more about how best then to choose

 

[Doom]

If you haven’t found this yet, go to

Berger Bullets Twist Rate Recommendations by Eric Stecker & Bryan Litz

In keeping with constantly improving the rifle shooting experience and providing the most accurate information we have updated our recommended twist rates.

bergerbullets.com

The

 

[Steel head]

Is there another formula for getting the proper bullet for steel targets?