Is this a new piece to you?
Very new but I know it's history (long story)
You said the hammer and pawl function normally with the cylinder removed, does the cylinder lock drop down as normal when the hammer is being cocked?
No, that cylinder lock will not drop down which is causing the problem. The lock remains upright when cocking (cylinder removed-cylinder pin in place) That lock can be depressed via finger pressure with the resistance of the spring that holds it upright being felt. The Hammer does absolutley nothing to relive the upward spring pressure. Does not feel that anything is loose and cannot hear anything rattle or get excessive play out of it. If the loading gate is opened though, that lock will smoothly slip below the base of the cylinder frame.
If the hammer does not free the cylinder lock and allow rotation then I would suspect either a broken part or erroneous assembly
I tend to agree but thought this problem might be of a more simple measure since that loading gate will free up the lock so easily. The gun has had less than 500 rounds through it (probably more like 150-200rds)
And has never been disassembled.....I Just Had A Horrible Thought But Would Have To Question The Bil & Nephew....You Don't Think That They Tryed To Fan This S/A Do You?

Thanks for the help, sounds like disassembly is in order.