No barrel manufacturing, but a lot of grit on stainless experience.
On stainless, 600 grit still has a visible trail while appearing "shiny" at angles. 800 starts reflecting better. 1500 grit on an otherwise clean surface is a foggy mirror. After 1500, a buffing wheel will get a clean mirror shine.
I have seen a stainless freak insert that looked no better than a 600 grit finish on the inside. The marks were very even at two angles, like it was honed going in and out. I don't know if that is common. I have a couple of old stainless barrels (TASO, 32 degrees) that appear to be around 1500 to 2000 grit inside.
What is sad is a mirror bore with a dozen waves in it.
I have often wondered exactly how they got those shiny bores myself. I always assumed it was some sort of full length slurry cut and polish.