If by breaking the breech you mean opening the gun, I have come across s handful of guns where the rim cut for the shell was not of sufficient width to allow easy extraction. That essentially locks the gun closed. The problem is more common with reloads. If that is your situation, look for bright scuff marks on the edge of the rim. Also, see if you can easily insert and remove the same shell(s) from the loose/dismounted barrels. That's one problem area and one place to start.