A few Colt HBAR barrels had chrome lined bores, but the chambers were chrome lined for reliability from what I've read. The easiest way to tell is to test the bore of your rifle near the muzzle with some "cold blue" solution. If it turns blue, then it is a naked bore. The chrome line HBAR barrels may not have shot as tight as the naked bore version, but I doubt I would know the difference.
I'm shooting a Colt HBAR 1:7, naked bore, chrome chamber, barrel for my High Power rifle, and right now I cannot shoot as well as the rifle. From the bench, with no sandbags, it prints under 1.5 MOA with irons at 100 yards. That is inside the 10 ring at all ranges for a High Power target. I have a Krieger on hand as a backup for when I shoot out the Colt.
You could probably do better with a scope and a real rest. But I would have no issues with another Colt HBAR, naked or chrome, for a service rifle barrel. A few years back a sniper wrote about his journey to High Master scores, all shooting a stock Bushmaster HBAR with a chrome bore and 1:9 twist shooting 69 gr SMK's across the course. It ain't the rifle sometimes, it is the shooter.
Machine guns are awesome until you have to carry one.