I Have around 20 some 22 smooth bores in my 22 rifle collection. Two of those are Remington 121s. Both my guns are marked "Routledge Bore For 22 Long Rifle Shot Cartridge". I have also seen at least one that was not Routledge bored and one that was marked for Mo-Skeet-O. A Routledge bore is when they ran a reamer down the end of the barrel to a depth of about 13.5 inches. The end result was for a better pattern. It made the end of the barrel look like a 410.\n\nRemington smooth bores and MO-SKEET-O traps and targets were sold together according to some of the original advertisements I have.\n\nAfter the 121 was discontinued Remington had a few variations of the model 572 some with Simmons ribs.