Quote Originally Posted by szvacek View Post
What size is that nut? I don't have an wrenches that fit it.
Steve,
That bolt and nut on your barrel band are not correct, it should have a screw that threads directly into the bottom half of the barrel band. Open this link and page about halfway down to see what your band screw should look like.

The U.S. Caliber .30 Carbines - Barrel Manufacturers