Or the 'rims' of the snap caps are a bit too thick for the guns chambers.
Does the problem still exist when closing it w/o any snap caps in the chambers at all? Is this hard closing problem only when a snap cap or fired case is in the chamber? How about a factory round or an empty chamber?
If it occurs all the time wether there is a snap cap or case in the chamber or not..
It could be a slightly warped frame from the case color rework,,,,or,,,
It may be the ejector springs (coil) have been replaced during the reconditioning. Springs that are a touch too long or the wrong dia.wire, etc will 'stack' at full compression and not smoothly allow the barrels to close while the ejectors cock. Plainly,,not enough room for the motion needed.
Even if the gun is not 'fired', each ejector blade shaft very slightly compresses it's ejector kicker at the last closing movement of the barrel pushing it past & off it's sear. So an improper spring may be felt as difficult closing/locking wether the gun is being closed after being 'fired' or not. Might sound silly,,but does the gun close easily & lock with the forend removed??
Once fired cases aren't the best for test purposes, especially a SxS as even one barrel to the next will vary a bit sometimes.
There's other possibilitys, but that's what comes to mind seeing the gun and the described problem.