The BAR-10 barrel is 4150 steel and is not chrome lined.
I do not view the lack of chrome lining as a disadvantage. I know there are those who think quite strongly that a barrel must be chrome lined, but I shoot a lot and have yet to shoot out a barrel - chrome lined or not.
As the BAR-10 is not full auto, I doubt I will view any degradation in performance for at least 50,000 rounds.
Obviously, the hotter the barrel gets with each shooting session, the faster the barrel will wear out. In full auto weapons, yes, a chrome lined barrel is an advantage.
Chrome lining a barrel can, however, adversely affect accuracy.
If chrome lining is a make-or-break criterion for you, then look elsewhere. But I think the BAR-10 is a well-balanced package even without a chrome lined barrel.