No need to shoot 10k rounds of steel case to justify barrel wear, whatever the wear may be compared to brass. Heck, a guy could buy a new AR barrel (link below) with every 1k rounds of steel case and still break about even compared to brass. Not that it would be required... just sayin'.

I would not fret over the barrel life unless it's a high-end barrel... but for someone who for whatever reason wants to shoot a ton of cheap steel case and worried about preserving their factory barrel: Anderson 1/8 for $85. Swap barrels and get happy with steel case if ya want. Mag dumps or whatever... get brutal on it all you want. Anderson Manufacturing 16″ M4 Carbine Contour Barrel Chambered 5.56 With A 1-8 Twist M4 Feed Ramps

All that said... I'd not worry about a thing. Just enjoy the rifle shooting what you want.

I'm seeing some ARs nearing $400. A case of M855 is over $300... kinda puts the cost of budget rifle parts wear and replacement in perspective.