I have several .223 AI's and .223's. Twists range from 1 in 12, 1 in 9, to 1 in 7. For light weight bullets up to 55 grains, the 1 in 12 is fine. For up to about 70 grains bullets the 1 in 9 works but a 1 in 8 would be as good and allow up to 75 or maybe 80 grain bullets. You need 1 in 7 or 1 in 6.5 to stabilize 90 grain bullets. I have had no problems shooting 40 to 70 grain bullets equally as accurately with the 1 in 9. If I was only getting one rifle, it would be a 1 in 8 twist for most versatility to stabilize 75 grain bullets and no loss of accuracy with lighter bullets. Benchmarck for lighter weight bullets and Varget for heavier bullets work fine for me.