Try some Shooters Choice Wipe out or Patch-out...it will out clean most of the other "copper cleaners" and isn't as hard on stocks etc. I use it all the time in dozens of guns...kinda messy if you're not quick on the button...READ THE INSTRUCTIONS and follow them...

Best if you pull the bolt and use the "tool" for cleaning lever guns advertised in several online catalogs.

Get the barrel slugged and measured to be sure, like Swany suggested. You might have to go to a larger dia hard cast lead bullet also.

Keyholing also suggests the wrong twist for the bullet length...

Yeah....172 gr bullets??????? Typo, er, what?.