It works pretty well.
 

Someone not too long ago asked a question about a bore light and someone else suggested using a .45 cal. stainless steel shell casing. I picked up a couple at the range yesterday, since I don't have a bore light. I have an old .50 cal. Thompson Center Hawkins and I've never seen the inside of the bore, so I dropped the casing down the bore, shined a small Maglite into the muzzle and PRESTO! After over 20 years I got my first look at the bore and it was BEAUTIFUL. It looked pristine to me. Pick one up at the range you visit and give it a try. I think you will be impressed.

A shiny dime works the same way.