Try shooting it first with a variety of ammuntion and see what it does before you get a new barrel. Is your rifle a pre-ban rifle? I could be wrong but I dont think Colt ever made
pre-ban barrels in 1/9". I really dont notice much of a difference between my 1/7 & 1/9 barrels when shooting the same ammo. As far as replaceing the barrel, any barrel from one of the larger companies such as Bushmster, DPMS, or Armalite will fit. Barrels can run from 185.00 and up depending on the configuration you want.