IIRC, the 20 gauge gun has a smaller bolt and doesn't need the notch in the right side, but it still has the hole in the left side to allow the latch pin to come out to the left. You should be able to see the pin in the bolt through the right side cutout and push it out when the pin is lined up with the left side hole. You might need a light to tell when that is, though.
Jim
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