twist rate question

[cdog]

I have a 223 with a 1 in 9 twist.
I understand the heavier the bullet, the tighter the twist you require.
I do not understand if it matters more of the over all length of the bullet that matters more, or the bearing surface?
I guess what I am really asking is if I had 2 bullets of the same weight, same length, but different bearing lengths, which one would likely stabilize easier?? Perhaps I have it all wrong, and if so if anyone would care to explain it in laymans terms I would greatly appreciate it.
The reason I ask this is because a friend and myself were debating which bullet my 223 would more likely stabilize, a 75gr amax or a 77gr hpbt. I beleive the 77 had a longer bearing surface by quite a margin?
Thanks for any and all responses,
Cdog.

 

[RA]

Go to www.shilen.com -- Click on barrels...then calibers/twists...scroll down to your cal...This is probably the best reference for what weight bullet for twist....I don't think that a 9 is quite enough for the 75 or 77 gr...doesn't hurt to try though....length will determine twist over bearing surface...Berger makes length tolerant bullets in the VLD style, but they are more fore clip/magazine feed problems when bullets are seated to the lands...the longer bearing surface will create more resistance thus increasing pressure, which will probably require a lower powder charge...this is all dependent on the bore dia., hence this is the reason that a safe load in your rifle may show pressure signs in others... there are many other variables also....hope this helps...Rick

 

[Twud]

http://sst.benchrest.com/shilentwist.html

 

[Aussie_bob]

If you go to this page, http://www.ssaamackay.org.au/Clip Art/bulletstabilitycalc.xls ) which i have added to our local branch website you can calculate the best length / Weight / velocity for your TWIST rate to totaly stabilize your projectile.