I did a check for you and all I found was foster type slugs by Lee and Lyman and Rapine. I did not see any rifled slugs out there. If your shotgun has choke tubes you could consider a rifled choke tube and use foster slugs. At shorter distances I have seen foster type slugs shoot great in smooth bores so that may be your only option depending on what shotgun you own. Jim

Are their any recommendations for molds for making cast shotgun slugs? I was after the slugs with the rifling built into the sides to use in my smooth bore.Any recommendations?

The rifling onthe side of a slug is put there with a die. It is not cast on. The ribs do help the slug pass a choke. They do not add much to accuracy. They fly point foreward only because they are behaving like a badmittin birdie. Spin aquired in flight has nothing to do with it. For a smoothbore gun with little or no choke I would experiment with balls. I have made and used pumpkin ball loads with good accuracy. I loaded them in shotcups. Real fun to shoot over water and watch them skip like a stone. Be real carefull with that! The Lee moud makes a thing that looks like a giant airgun pellet that goes in a normal shotcup and crimps like a normal shell. That one intrigues me. If you are going to play around with slugs I would suggest a rifled barrel.

The Lyman hourglass slug is the one we get the best reports on. It fits inside a shotcup that acts as a sabot. I've had very little success with the others.

I wanted to use them for hunting pigs. I dont have a shotgun with removable chokes yet ,but will think about a rifled choke later on. I have used the factory slugs which have the rifled ribs on the outside. And yes ,they did seem to be like a badminton design. Its this sort of thing that I was after ,just for close up hunting. I havent used or seen the "hour glass"shaped ones yet.
I will look through some of the mold manufactures websites to see if there are any molds to make the badminton shaped ones.(Sorry I dont know the proper names)