Hey Peter, As you know I just started shooting this year, Coach Bunker set me up with the bore guide I am using on the 40X and the Kodiak. After familiarizing myself with how to properly use it, I sort of came to the conclusion that only by misusing it could I do any damage. Essentially, as has been mentioned, by running the jag or brush out of the muzzle too far and damage the crown on the way out or coming back in. To try to help make it idiot proof,(for me), I fabricated a little "stop" that goes around the rod(mine is a 44 inch Dewey), that runs up against the back of the bore guide and has a set screw, this determines how far the rod can go into the barrel(and therefore how far out of the muzzle). Works good so far. If it could only help turn some of those, good X count 249's into 250's. No that's a different issue! Now I've done it, given away the first in my line of benchrest accessories, its "use" would benefit the benchrest world, and its "sale" would benefit the poor here in Maine (me).Well, maybe not, on either counts. Cheers Charles