We carry a variety of 9mm BCG's for your AR9 build! You dont have to choose between a Colt or Glock style 9mm AR15 because both Kaw valley and New Frontier make a modular 9mm bolt that accepts both style magazine. 9mm AR's do not need gas system parts, such as gas tubes or gas blocks because AR9's operate on a blowback system. Because of the blowback system it's a good idea to choose a heavier bolt carrier group and buffer. We carry all of the buffer parts that you need to help your 9mm blowback BCG run smoothly. If you're going to dedicate your build to using Colt pattern magazines, such as the Metalform 32 round magazines, then you can use one of our CMMG MK9 bolts. And if you want to leave your options open and start collecting parts now, you can grab one of our modular 9mm bolt carrier groups and decide later on which type of magazine is best for you. Either way you can't go wrong as Glocks 32 round magazine has proven to be just as reliable as Colt.