There's a misconception that the hard chrome lining of gun barrels is like bumper chrome.
Bumper chrome is/was thick and soft and had to applied over a copper under layer. Anyone who had a nickle plated .357 and fired a lot of hot loads saw the plating disappear from the front of the cylinder.
By contrast, hard chrome (and it's various patented variations) generally runs 72-72 on the Rockwell C scale. It achieves a bond with the parent material on the molecular level without underlayment. It's also less than 0.001 inches thick, frequently 0.0002 inches. That's much less than the allowable variation of bore/groove diameter in the average gun barrel. There would be little or no need to produce oversize dimension barrels with that type of plating
I can't speak to the difficulty of achieving an even plate in a barrel bore. I do know that platers go to extreme effort to do so. The definition of "even" also makes great difference. Exactly how many significant zero digits are there after the decimal point?
FN, amoung others, is producing precision rifles with plated bores. Judging by the groups achieved by many folks in T&E of the rifles, if there's a negative effect, mere mortals can't detect it.
This isn't to say that all plated bores are created equal. I noted an AR builders ads for "extra thick plated bores" in some of their barrels. "For high volume shooters" I have to assume those were either a mistake or someone was trying to build oversize bores/grooves to acceptable dimensions.
