If you're talking about the bluing on the metal, there's nothing you can do to "polish" a dull blue job.
Any attempts to polish it will only thin or strip off the existing blue.
Attempting to use a metal polish will damage the bluing since all metal polishes ARE abrasive.
That's what metal polish IS.
About the only thing you can do is clean the metal as well as possible to get dulling dirt and fouling off.
To do this, apply a coat of CLP Breakfree and allow to soak over night.
Wipe it off the next day, and the metal will be cleaned of any dirt.
After cleaning, what's there is what you've got.
Further "cleaning" will only further thin the existing bluing.
To protect the metal without using a lube, use Johnson's Paste Wax to wax the metal.
I don't recommend using car wax since many contain abrasive to polish the paint and will damage bluing.