Over/Under Question

The only O/U that will accept different barrels (other than dedicated skeet sets) that I can think of is the Valmet. It's a European gun that has a whole selection of barrels, including shotgun/rifle combos - kind of like the Thompson Center line. I used to see them advertised back in the 90's but haven't seen one in years.

The problem with interchangeable barrels is getting a perfect fit between the barrels and the receiver. With a 4-barrel skeet set, the barrels are all fit to the receiver at the factory. You could probably get different barrels for most any O/U but you'd have to send the gun in for fitting.

There are other O/U setups but not the way you are looking for them. Most of the ready mades are particular to a a segment of the sport. There are 2 barrel sets that come from the factory for trap (as an example) where there is a top single barrel and have a double barrel replacement so that you can shoot singles and doubles with the stock/receiver.

The Valmet was supposed to be the gun that changed all that. You could buy any configuration you wanted and add to it as the need came up. I had one of the first ones on the market and it was a so-so gun at best. I still see them from time to time at gun shows.