In a .223 caliber is a 1 in 12 to little twist for good ballistics with a 60 grain bullet?

no,....shilen says a 12 twist works for bullets up to 63gr.

I have seen 60 gr Sierra hp work in a 1-12.
A 1-7 will also shoot 60 gr at 223 velocities.
Now days,why limit yourself to small bullets in a 223 due to slow twist

At velocities less than 2800 FPS 0.603" to 0.654" for a 1:12

At velocities greater than 2800 FPS 0.723" to 0.785" for 1:12

"At velocities less than 2800 FPS 0.603" to 0.654" for a 1:12

At velocities greater than 2800 FPS 0.723" to 0.785" for 1:12"

Steve - where do 0.655" to 0.722" fit in your rule ?

its the length of the bullet, not the weight you should be interested in. In larger cal. the copper bullets make a difference.

As 243 stated, it is not the weight of the bullet, but the length.

The numbers I quoted were length of bullet for a specific twist.