The thing that doomed Metford barrels was the combination of the enormous heat generated by Cordite and the incredibly hard nickel jackets allowing these hot propellant gases to bleed around the hard bullet in the throat.

If you ever look up a G3 barrel, it looks like a Metford; sort-of "shot out", from the factory. The differences are that the 7.62 NATO ball projectile is a very close fit in the polygonal rifling "grooves" AND modern double-based propellants burn much more slowly (relatively speaking), and at much lower temperatures for a given presure, than the old Cordite. The hard-chrome lining is handy too. Arisakas also have this "pre-worn" looking rifling.

If you have a "nice" Metford and want to shoot it, look for recipes involving gas-checked, HARD cast bullets in the 190-200gn range. See also; hints regarding Teflon tape as bullet lube.