I have a 1:9 M4 that I have shot 55 grain bullets through very well for years. I am seriously thinking of buying another AR thats a top tier M4 which has a 1:7 barrel. I have a ton of 55 grain 5.56 stored up. I know the 1:7 will shoot 62gr green tips well, but does it also do well with 55's because I don't want to have to buy more separate larger ammo anytime soon. Thanks for any info! Wanna kill these ads? We can help!