1. You could use a razor saw, and very carefully cut the barrel lengthwise at the glue joint, then try regluing.
2. Try scribing the glue joint with the back of a #11 knife blade, and then carefully try to pop or pry the halves apart. With any luck, the glue didn't get into the whole thing.
3. Place putty along the glue seam, and then use a flexi-file to get it into a round shape.
Hope this helps some.
Gip Winecoff