I wouldn't recommend a file, one swipe may be too much, it's better to use a stone, that way you won't take too much off at a time, if you do, the barrel won't lock up tight. A stone is the better choice, it's also easier to keep it flat since it's not as aggressive. If you don't have a flat stone, use some 400 or 600 wet/dry wrapped around a flat file.
Hillbilly, I have several Mueller scopes, 6 to be exact, I have the Eraticator on my 204 Ruger Handi, haven't killed anything but paper with it, but it does that extremely well!!
No groundhogs here, in fact no varmints within about 100 miles of me!!
Tim