You don't say exactly how they "don't fit". For guns of the period yours are stocks should pretty well be interchangeable between any K, L or X frame. They may not fit precisely around the perimeter, but would be close. On K frames the grip angle, shape, stock circle shape and stock pin hole position has not changed, except within manufacturing tolerances, from 1899 to today. Before someone inevitably points out that there are both round and square butts, this comment applies equally within either grip frame shape.
Unless you are sure both of your guns came from the factory as round butts, it is possible someone has re-shaped one of them from square to round and wasn't too careful about accurately duplicating the factory round butt contours when doing so. This change is somewhat common if you follow this forum for any length of time. At least many ask if it can be done and others always tell them it can!
