Hoppes #9 will work, but you've got to use a well saturated patch, get the bore nice and wet, and let it sit a while.....say 10 to 15 minutes.
Even better, if you can find some, is military GI Bore Cleaner.....that's what it was made for.
When in doubt, always assume
ammunition is corrosive.
Here's some good advice on cleaning your rifle....