neat family history stuff there bill. if there is no loading port on the revolver then you would have to push out the wedge, slide off the barrel then the cylinder. it might even be a rim fire. if it is a percussion a bench mounting loading tool could be constructed. after saying all that it would be best to just to leave it be.
...the jap is either a 6.5 or a 7.7. mauser more than likely 8mm. those rifles would be sturdy enough to shoot. I would just make sure the bore and chamber is clean. no wasp plugs etc. once again neat. bobn