For some reason I just can't wrap my mind around the whole twist rate topic.
I am concerned with .223 Remington ammo.
A 1/9 rate spins the bullet one revolution in 9"?
A 1/12 rate spins the bullet one revolution in 12"
A 1/9 rate is "faster" than a 1/12 rate?
Light bullets need "slower" twist rates?
Heavy bullets need "faster" rates to stabilize?
A 1/9 twist in .223 will handle what range of weights?
A 1/12 twist in .223 will handle what range of weights?
I am looking at a CZ 527 with a 26" heavy barrel.
Am I even close on any of this or have I got it all basackwards?

Yes, the 1-9 will handle 70 grain best, but will be able to shoot 52 grain also. 1-12 will probably shoot 52 grain best but will also shoot other weights also. At 200 yards you could shoot almost any standard weight well in either rifle. In the 1-9 I shoot 52,55 grain and can hit baseballs at 200 yards. In the 1-12 I just shoot 52 grain and get good groups at 200 yards and it is a bolt action the 1-9 is a Ar15. Good Luck

There really is only a very, very minor penalty for spinning a bullet "two fast". It accentuates bullet imperfections, and reduces flight characteristics at (very) long range. Thing is, at VERY long range (say 500 yards and more), you would only use the heaviest bullet you could, so the whole point is moot.

One thing to remember, it is not the twist that stabilizes the bullet, it is the rotation of the bullet that does. Rotation is a direct function of the speed of the bullet and the twist of the barrel.

For example, I can easily stabilize 80 gr. VLD bullets out of my 223WSSM with a 9 twist barrel. In a 223Rem, that would take a 7 twist.

In 223, a 9 twist will handle EVERYTHING up to the 69 SMK. HTH, Dutch.

Remember also that necessary twist is actually related to length not weight. For example a 60 gr spitzer being longer would need a tighter twist than a 60 gr round nose bullet.