Think of it this way. When the barrel is rifled, the cut rifling is very crrisp and sharp. Chrome lining is a plating that is applied over the rifling.
It is extremely hard and durable, thus increasing barrel life. The Melonite is a metal treatment, kinda like bluing a pistol frame. It also hardens
the barrel and offers outstanding corrosion resistance. Since the Melonite is a treatment it does not effect the rifling it is left as precise as when
it was cut.
A Melonite treated barrel is said to have a life that of a chrome lined barrel, possibly longer. I have not seen an definitive number.
A standard chrome lined barrel will last 12-15 before throat and gas port erosion effect accuracy. However there are reports from
defensive carbine instructors of barrels approaching 40k and still acceptably accurate.