Bent cylinder pin
Well, when I returned the gun, the Gunsmith had to remove the barrel. It was he who diagnosed it as a bent cylinder pin. The last half inch or so of the end of the pin is bent, so that the cylinder slides on and spins but the barrel was obviously forced on so that that it could only be removed with tools. When I looked at it later, after the gun had been returned, I held a stainless steel rule against the cylinder pin and sure enough, the end was bent. Maybe when the gun was manufactured, the cylinder went on first, then when the barrel was pressed on, the installer didn't take the time to see if it could be removed? Maybe the lunch bell rang, who knows?