Many use trade names, but it's all hard chrome.
Prices vary from supplier to supplier, and most offer options as to final appearance.
Appearance can range from the original satin lightly bead blasted "orange peel" pearl-gray, to a brushed stainless look, to a full mirror polish.
At least one, Armoloy of Fort Worth, offers plating inside bores and chambers. One other plater said that he though that didn't really do much.
With new gun finishes coming available, and some disappearing soon after, still today if you ask most custom gun makers for the best possible finish, they recommend hard chrome.
Cogan says the ultimate gun finish is hard chrome over stainless steel.
Here's the top hard chrome plating suppliers.
APW/Cogan is probably the best of them all and the best all-around gun refinisher.......
https://apwcogan.com/
Ford's used to offer top line bluing, but recent review say that their new polishers are not up to snuff and should not be used to do re-bluing.
They always had a great rep for plated finishes, but if a gun requires some polishing, approach them with caution......
Ford's Custom Gun Refinishing | Crystal River, FL
As above Mahovsky has been doing hard chrome for a good many years and offers the lowest prices. Note that communication is often rather poor and recently there's been a couple of reports of quality issues.
Hard Chrome Plating & Electroless Nickel Plating, Armalloy & Gun Bluing by Mahovsky's Metalife
Techplate offers about any metal finish available, and does hard chrome on guns. Some complaints on workmanship have been reported.
Tech Plate
Armoloy was the first to offer hard chrome to the general gun public. I used them extensively for years, but had some problems with guns developing gray blotches.
I stopped using them after a "stolen" customized Colt Combat Commander gun that they never fully made good on, and didn't want to report as stolen until I had to get the BATF involved.
They do advertise plating of bores and chambers at extra cost.
Armoloy® TDC - Armoloy of Fort Worth, Texas