Have Firearms Repair Questions? Ask an Expert
It sounds like the locking block on the bolt is not fitting into the opening of the barrel extension.
When the bolt is fully closed the locking block cams up to lock the bolt in the closed position. Make sure there are not any burrs on the block or the opening in the barrel. One may be out of square from being forced. If this is the case use a file to square the opening and block.
Let me know how you make out with it.