Smells fishy.....side stamped serial number....usually means Remlin, JM stamped barrel that looks bit wonky. Hmmmm.
I've seen a lot of weird looking JM stamps, I also heard for a brief time there were Remington made guns using up the last of the JM stamped barrels.
I can say positively, I would not want barrel made in the last days of Marlin.....and certainly not in the early days of Remington making them
I have a 1894 .357 made a few years before the Remington buyout of Marlin with the serial number stamped on the side of the frame....JM stamped.
