This is from Shilen barrel's website.
.224 CF
- 7" for bullets heavier than 70 gr.
- 8" for bullets heavier than 70 gr.
- 8" * Ratchet rifled 4 groove
- 9" for bullets up to 70 gr.
- 10" * for bullets up to 65 gr.
- 12" for bullets up to 63 gr.
- 14" for bullets up to 55 gr.
- 14" * Ratchet rifled 4 groove
Here is a twist rate calculator that may help
http://www.realguns.com/calc/riflingtwist?results
