It sounds like a trap barrel to me. I've seen several of those types of barrels on the trap range. The length of the barrel makes for a smooth swing and easier "follow through" on the shot, and I imagine the longer sight radius helps, too. Couldn't say what the angle of the high rib is for, but I'm sure someone else can fill us both in.
In trap, the shooter typically stands 16 to 25 yards from the "trap house", from which the clays are launched. There are five positions side by side from which to shoot, and the shooter moves to a different position for each shot. The clay, usually just one, flies away from the shooter at various angles.
In skeet, the shooter fires at two targets each time, one comming from the left, and one from the right. One clay is thrown from a "High House" and the other from a "Low House". There are more shooting positions than there are on a trap range (can't remember how many!), and they're arranged in a semi-circle from one house to the other. The distances for skeet are much shorter than those in trap.
That's the gist of it, and I'm sure there are lots of variations on these themes, but I'll leave that up to other, much more experienced, TFL members.
-boing
