One likely possibility: The ejector rod is/was loose and has now unscrewed itself just enough to prevent the cylinder from opening.
The solution: Easier to accomplish than explain... First, the threads are LEFT-HANDED. Next, you have to turn/tighten (COUNTER-CLOCKWISE direction) the ejector rod just enough to allow the cylinder to open. Then, ideally, once the cylinder is open, remove the ejector rod (watch/catch the springs), clean it, apply BLUE locktite to the threads, and reassemble.
Note: A small, plastic or brass, wedge-shaped tool (like a screwdriver) might be needed to assist in turning/tightening the ejector rod before you can open the cylinder. Avoid any temptation to use a needle-nose plier or the like; that will lead to (at best) scratching the ejector rod. Just tighten it enough to allow the open cylinder to open, then you're home free. (Patience is a virtue, don't you know!)
Hope this helps. Good luck!
