A cracked barrel nut can lead to headspace issues. Not good. Cheap fix with a go gage and barrel nut wrench. If you can get the nut off easily, a strap wrench can tighten the nut correctly. In the past I have swapped several barrels for friends and family. Most swaps are simple, but I have had a couple of barrels that the nuts were frozen on because of bluing salts in the threads. Not a common problem though.
