Chrome lined bores are just that. chrome lined bores. I could only guess that the chrome plating occurs straight after polishing and prior to barrel join in the case of a sxs.  I don't know but that would almost seem the best manufacturing approach.

I cannot proclaim to know the specific process nor the specific spec (what type & what class) but typically an allowance of .00001 is all that is necessary unless a drawing specifies a thicker application.

That .00001 is designated as the dimensional allowance for buildup per surface so on a bore or any other round surface - an allowance multiple of 2 would apply…in other words a bore that requires an accurate size will have to be over-bored/polished by .00002 to allow for the plating which would then bring the item into spec.

What does that mean in this particular application from a dimensional/manufacturing perspective?. exactly nothing, since shotgun bores do not require precision, nor do manufacturers bother to focus upon that due to  alack of necessity relative to functionality.  Manufacturing money (labor) is better served elsewhere.

One of the key considerations when making preparation for chrome, is the material finish prior to plating because chrome will bring out every flaw upon the surface; but this is only an aesthetic concern.

That said, and from a practical view relative to bores in firearms, bad surface finish = harder cleaning because the residues tend to occupy the space below the surface (metal imperfections) therefore a smooth bore is easier cleansing.

A common misnomer is that a “good finish” must shine, that is not true at all as many a dull appearance possesses a very fine surface finish throughout all of industry.

The application of chrome in shotgun barrels is a fantastic marriage of benefits; it’s hard, it resists corrosion, it’s slick, and it cleans up very easily.

If the chrome plating is desirable to a Parker Reproduction owner, any modification to chambers, bores, or forcing cones is a no-no because even with simple polishing the chrome is gone, with exceptions.

A wadded up piece of Nevr-Dull, or other non abrasive polish, at high speed won’t touch it.  That will just polish the surface, making it just that much easier to clean provided the regimen is maintained periodically.

The only exception to chrome lined barrels amongst the Parker Reproductions are the 16ga barrels as supplied by Krieghoff which do not “appear” to be lined.

Chrome is nasty stuff for the folks who work with it day in/out.

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