I just checked my 15-2 in .357 for you. Properly set up (0.005~0.006") barrel to cylinder gap gives me about 0.001" spring tensioned endshake unloaded. It actually reduces slightly with (dummy) rounds loaded.
I'm guessing the old owner didn't know how to set the gap & had it too long then brought the ball in the rear forward to try to remove it?
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Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”