Asking for a friend... Rusty bore issue?

[poker]

Regardless of what cleaner you go with; pick up one of these, it looks like a brillo pad but (they say) wont hurt any bluing but Will remove rust.
Now it's not going to 'sand' the barrel but somehow it Does scrap the rust off.
I have used it to recover two barrels now that came to me with soarly rusted barrels, one was pretty bad.
Expect to use some elbow grease, but I didn't have to remove the plug.

I cut a piece and wrap it on a suitable down using twist wire, then just scrub away, adding some cleaner, the oil

https://www.big45metalcleaner.com/

If you turn any of the softer grades of stainless steel in your lathe, or know machinists who do, just take and bag up some. It accumulates in the pan pretty fast. It works pretty decent to scrub light rust off the outside of a barrel, but so does plain old aluminum foil. The key is to be softer than the bluing but harder than the rust. For in the bore Id prefer a scotchbrite pad wrapped on a jag

 

[N.Y. Yankee]

Rusty Bore was my NASCAR name.