The 1:9 twist is perhaps the most versatile of all the .223 twists. It can shoot bullets up to the 75 gr. Hornady A-Max; and still group pretty well with bullets in the 50 and 55 gr. weight range. Obviously if you were going to shoot only 55 gr. and lighter bullets, you would choose a 12" or even 14" twist. But I have been amazed at how well 9" guns will often shoot bullets like the 50 gr. V-Max.