I was going to post this in another thread but exploder crashed like a Ford on Firestones.

This is some of what I've gathered on twist rates going around.  Bullet weights, and etc.

.224 twist rates for 55.6 Nato / .223 Rem.

1:14 - Restricted to the very light bullets under 55 grains.  Best with specialty lightweight varmint bullets in the lower weight category.  30gr to about 50gr.  Usually found in purpose-built rifles.

1:12 - Not as restrictive as 1:14.  Can possibly stabilize 55gr standard FMJ but doesn't excell at this.  Most accurate with lighter bullets in the 35-50gr range.  More common in bolt-action varmint rifles.

1:10 - More universal.  Could stabilize up to 62gr but excells at the medium weights from 40 to 55 grains.  Much better with 55gr than 1:12.

1:9    - Considered by some to be the most universal twist rate.  Usually won't dissintegrate the lightest bullets (though if you read ammo oracle you'll see other issues) but will stabilize the mediums just fine.  40gr - 64gr (and one report of 70gr) should stabilize.  Bullet shape and heavier weights may dictate a 20"+ bbl for maximum velocity.

1:8    - Not as universal as 1:9 but still very good.  I have not heard a report of an 'off the shelf' available load dissintegrating.  Best with 55+gr.  Check bullet construction and research projectiles lighter than 40 grains.

1:7    - I have heard tales of projectile destruction with a variety of weights in this twist rate.  I'd check construction history on anything lighter than 50 grains.  If you must stabilize 80 grains here's your twist.  Note that COL might be an issue in the heavier projectiles.

*edit*
NOT to be taken as cannon.  These are my observations and I FULLY INVITE comment or corrections!

OK I know that my Bushy SPRMINTER 1in9" 24" shoots 75 grains BH perfectly. I read a artical in and old G&A Mag once about a guy that took a 26"barrel and cut it down every few shots and inch, and the results did not change that much .