I have a 1974 Browning Citori. I just purchased it and I am just finding out now that there is a good possibility that the dirty under barrel actually is pitting.
If it is pitting it really is mild. I guess first of all are the barrels chrome lined and if it is pitted can I polish the pitting out?
Pitting is caused by rust eating into the metal and shows itself after the rust is removed. Pitting can be buffed out but you lose all the surrounding metal when doing so. If the bore is pitted there isn't anything you can do except clean the rust out and keep it oiled so it doesn't get worse.