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!!
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No groundhogs here, in fact no varmints within about 100 miles of me!!
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Tim