I'm in the process of building a long range AR. I have the gun 90% together, I just need a barrel, muzzle device and scope mount. I was thinking of either an 18" barrel or a 20" barrel in a medium profile configuration. What does the collective suggest for a barrel? I already have a gas block (.750) and rifle length gas tube for it so I need it to be within those confines. I'd also prefer a wilde or 5.56 chamber and 1:8 or 1:7 twist for shooting the heavier bullets. Just for those that are curious, the rest of the build is as follows: BCM upper, Palmetto State BCG and HPT/MPI bolt, standard charging handle, Midwest Industries SS series 15" rails. The lower is a Palmetto State Armory lower, DPMS LPK, Magpul MOE Stock, Wolfe reduced power trigger and disconnector spring. Also, any suggestions for a scope mount?