Jim, my thinking and understanding is that "chopper" lump barrel and lug construction is nearly always associated with sxs but not limited to nor defined by the presence of two "half lumps"--one protruding from each tube of a proposed barrelset before striking and milling. The mental picture of "chopper" is preserved in the lower barrel of an o/u constructed such that there is a single protruberance integral to the forging before milling; admittedly--in the case of the Miroku-produced 325--after milling it "looks like" three: barrel hook and two "bifurcated" recoil lugs with lock recess. A monobloc with an integral lump would lack the lever arm or "handle" to easily suggest chopper, hatchet or meat tenderizer to the visually imaginative but would, imo, contain the necessary and definitive attribute of construction from which the chopper image was derived. If the tube or tubes were socketed into the monobloc prior to milling the lugs (probably not likely in the production sequence) the assembly would indeed suggest the quaint image of the "chopper". Strange to say, I've had three Supers and access to Schwing's book and never gave "chopper lump" Supers a thought--probably too fascinated with the forend mech.
jack
