Dave, good to see something written about a great plug. Atom Jr was the first swimmer that my mentor, Jerry Bernard, showed me how to work. He would tune the nose wire down to have it swim slowly on the surface and about every 10 feet of retrieve he would pull the the plug across the surface and splash it. Not unusual to have a bass react to the pop. He never altered the lip.
I visited Bob Pond at the factory once and the Juniors came into conversation. I was curious why they went from 1 3/4 oz to 2 1/4 oz. He said the brass molds were getting worn and they retooled them making them produce a slightly larger plug.
The Junior was the first plug i skinned and it was a go to until I discovered the Super Strike Popper to carry the skin, but that’s another story. I favored the Atom 40 and 54B swimmers over the wood versions. They seem easier to tune, I think because of the lighter weight lip. Only downside to the 54 was that it would chop or crack if you hit it on a rock.