Some people will tell you that a 1/7 twist is only good for bullet weights above 55 grains. It is a common myth and spread all over the internet that to get good accuracy out of the your ar15 with the most plentiful ammo, buy a 1/9 twist. This is a myth that has been repeated so long it is widely believed. The problem is, the people who tell you this never test it. The truth is the 1/7 is the best of all worlds. You can shoot very light stuff. As light as you would care to shoot anyway. And you can go all the way up to 80 grains.
Above is a target I fired 18 rounds of 40 grain hornaday V-max bullets at 100 yards. The orange dot is 3/4 inch in size. I can not get accuacy much better then that when that many rounds are fired and using a milspec trigger. The rifle was a factory Colt 6940 using nothing more then sandbags for rest and a 18x leupold target scope so I had nothing to blame on the group size. If you got a 1/7 twist and want to shoot bulk cheap 55 grain ammo, or remington or winchester brand bulk 45 grain ammo from walmart do not worry. Go for it. barrel quality, ammo quality and your own skill may make the groups bigger, but it will NOT be because of the twist of 1/7.