schuetzen - I don't think there was a smooth bore 12 ga ever offered with a vent rib. I have a 12 ga field barrel with a screw in choke, and some 12 ga smooth bore slug barrels. I think the only choke for the field barrel was in full, so why insert choke tubes? Today I found an old magazine article. It was an April 1983 article by JD Jones, the guy who does a lot of Contender barrels. He said there would be a number of rifle calibers for the TCR and a 20 ga shotgun barrel with a vent rib. The rifle barrel's monoblock was probably large enough for a 20 ga shotgun, but I do not think any were ever made. It was probably several years later when Thompson-Center came out with the 12 ga shotgun barrels which had a larger monoblock. The three types were the field barrels with an insert choke in full choke, a smooth bore slug barrel, and fully-rifled slug barrel. I do not think that a 12 ga barrel with a vent rib was ever made. However, one could have a vent rib TCR barrel made. - DON