Perhaps the chrome lining simply increases barrel longevity.
Spot on statement Sir.
Machining a barrels material is allot easier when it doesn't have to meet Rockwell hardness. Cheaper to chrome line a barrel than to alloy the steel with chrome at the foundry in order to get the same results. Chrome coating or liner takes all the abuse. i.e. corrosion, friction, and heat all in stride. Chrome is still considered one or the hardest materials known to man even to this day.