Well many HBARs are .750" and the old pencil barrel is .625". There is a government profile that's a combination of both and it's not necessarily an M4 profile. In a 16" barrel the pencil/LW can be about a pound lighter than the HBAR.... I am looking at a 16 in. barrel, but I know I do not want a mil spec m4 barrel or a .950 dia. bull barrel.