Chrome lining is a process used to protect a rifle or shotgun's bore with a thin coat of chromium, generally applied by electrical plating. Some curse it, some love it. The curse is that the plating process doesn't allow for the same precision in bore diameter, but the protection provided is exceptional...the controversy goes far enough for some auto weapons to have a chrome plated chamber but un plated bore...thus making auto function more reliable and any concerns about the accuracy of the bore are removed. Frankly, one issue has made me think that any trade-off might be of concern to a benchrester, but not to most of us...
I recently was given a WWII Japanese 7.7 rifle that had been left in a barn since the 50's. It was a complete ball of rust and had spiders an critters living in the bore. I cleaned it up in an effort to make it a wall hanger (it was that bad) when I got to the bore, I wasn't even going to bother, but did want the critters out, so I pushed a patch with Hoppes through. All kinds of junk came out the other end with the patch, but the bore was completely shiny and like new due to the chrome plating. Pretty much all SKSs and AKs have them also.
regards,
graycg