When we talk about "polishing" gun parts we DO NOT mean "like a mirror".
What we really mean is to SMOOTH parts.
The idea is to level any machine marks that might cause rough operation. All that's needed is to smooth the part just enough to prevent any catching or roughness.
All machine marks or roughness does not have to be removed.
So, why do custom guns have bright and shiny feed ramps??
Because the customer pays for a "polish job" and if he can't see his face in the mirror-like surface, he thinks the gunsmith either forgot to do it, or ripped him off by charging for something he didn't do.
The difference is, a real gunsmith can do a mirror polish job without ruining the part.
You know the job is done when it's smooth enough not to catch or cause rough operation. It will not be bright and shiny like a mirror.
That usually means that if you run a fingernail over the part your nail will not catch.