I have an old 20" 1-14" twist barrel that I was wanting to flute to make a lighter weight free float coyote upper with. I mostly shoot 50gr v-max out of it so I'm not concerned about the twist rate. Its also not a tack driver so I'm not worried about screwing up the accuracy by fluting it. The area under the handguard forward of the chamber is .850" diameter and the area in front of the gas block is .725" diameter. My thoughts were six 1/4" wide flutes .140" deep under the handguard and six 3/16" wides flutes .105" deep forward of the gas block. This brings the bottems of the flutes down to around a .570" diameter under the hand guard and .520" forward of the gas block. The same areas on a colt m16 pencil barrel I have is .640" under the handguard and .570" forward of the front sight. I did find a company whos thinest barrel was .550" after a 2" taper from the chamber area, and again .550" forward of the front sight. AR15BARRELS.COM - Featherweight Barrel Profile What are the number of flutes, widths, depths and diameters of your fluted barrels? Just wondering before I order some ball end mills.