Gary;
I assume this a single hook gun. If so the pin in the bbl lug rides inside the hook for cocking. In disassembly you have to make certain the bbls are held back against the face as you open them to insure the pin clears the end of the hook. Another thing to try is to un-cock the gun before dis-assembly which keeps the hook down tighter in the frame bottom. If it has the three position safety as do most Lefevers this is easily done by opening the gun which pushes the safety slide to the rear fire position, then simply hold the triggers while closing. Then snap off the forend & see if it will come apart. Lefevers should be able to assemble & dis-assemble or have the forend removed or re-assembled either cocked or uncocked, so no problem with this. They do sometimes though dis-assemble easier with the hammers down than cocked.
