Best examples of a barrel shooting 1 MOA all day long, or at least for many, many shots, are the test barrels used by Lake City Army Ammo Plant testing M118 or M853 7.62 National Match ammo lots. They'll put 200 to 300 shots in a single group. Their best lots' group have a mean shot hole radius of 1.7 to 1.8 inches and the extreme spread's under 6 inches. Tests are done at 600 yards, so that's MOA all day long to me.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master