Adding 20ga bbls to a 12ga frame is a very common practice esp for entry level guns. Not only pumps but this is done on SxSs, O/U and semis. Heavy shotguns are no fun for beating the feet upland use.Guntech can you explain this a bit more for me . When you say a Remington 870 20 gauge Lightweight is built on a true 20 gauge frame does that mean some 20 gauges are built on 12 gauge frames ?