I used to visit lots of plating shops in a previous job.
Cosmetic chrome plating on external surfaces is rather easy. The problem is, most shops do a standard buffing and then acid pickle before copper plating, and then nickle plate, and then chrome as the final finish. If metal preparation is not carefully done, lines, eges, and lettering come out blurred and overbuffed, like bad quality re-bluing. Screw holes and critical dimensions have to be preserved with clay plugs or masking.
Plating the inside of a barrel is another matter. It is very tricky, and involves suspending a metallic rod inside, held at both ends with insulating washers. Acid pickle is used to prep the steel surface, and then layers of plating as before.
The actual plating thickness usually exceeds 0.001" thickness, so for critical surfaces, that much steel must be removed before the plating.
Hard chromium plating on the other hand, is much more durable and suitable for firearms, such as the insides of military gun barrels and sporting shotguns. THAT really requires a shop that specializes in it. Expensive too.
None of the chrome plating systems are really suited for the home hobbyist because they require solution agitation and heating, and careful control of the chemistry.
HTH
John
