I'm looking at Carlson's extended tubes for two guns: Citori and a Rem 1187. Checking both on the cabelas website, I notice that the tubes for browning start off .010" less restriction than those listed for Remington. Example: Browning "cyc" = .740", while the Remington "cyc" is .730". Thats a two choke size difference! Now I'm wondering what is the actual size of a 12ga. ?? Why the difference, and which tubes to get for skeet and which ones for clays? I don't care how they're listed, but would like to know what sizes are best for skeet/clays. Thanks.