If the cylinder will not rotate on the shaft with the yoke dismounted from the gun you almost certainly have a serious debris problem or a really bent ejector rod.
Try trickling some good lube, like CLP, down the ejector rod from each end of the cylinder. if that doesn't work you may need to disassemble it. It helps to have a special tool so you don't damage the shaft. It almost certainly has a reverse thread on it.
Most firing debris is powder, it is carbon based and you need a LOT of it to totally gum up the works. Could concieveably be a chunk of jacket, a chunk of lead, or even some sand or range crap.