I've had five 223 Rems and one 5.56 all with 1:9 twist rates. All shot 40 grainers up through 69 grainers the same and quite well. I currently have one Savage in 223 Rem with a 1:9 twist 26" barrel. This gun will shoot any weight bullet under a half inch at 100 yards all day long. I have yet to see a 40 grain .224 bullet get over stabilized.