You cannot put the standard 20 ga barrels on a 12 ga receiver, because they use different reciever sizes. Cole can make you some 20 ga barrels that will fit, but there are no "deals" on them. Prepare yourself for sticker shock!
You would be better off getting a set of Briley subgauge tubes to go in the 12 ga barrels, or just buy a 20 ga gun.
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