What are the main differences between over unders used for trap, skeet and sporting clays. I only ask because I'm looking for an all around o/u and in the Classified ads people will post "trap gun for sale". Also any suggestions on what to buy for around the $2000 mark? I want something I can use for all three disciplines. I got to try a browning xs skeet a month ago and loved it but can't find one for around 2000.