If it has a solid rib and a narrow schnabel type forearm, it is just a solid ribbed Champion, which came with a bit of checkering on the grip and forearm. It was made in 12-, 16- & 20-gauges and later years also .410-bore. The Special Trap with the ventilated rib was only offered in 12-gauge. Most Iver Johnson catalogs are undated, but the first I have that shows the Special Trap is A-29, which also has the Super-Trap, the vent ribbed, beavertail forearm version of their Hercules double.