AISI 303 stainless usually contains "high" sulfur or selenium to make the material easy to machine. The same elements added to the base metal cause hot cracking when it is welded.
I've encountered problems with weldability every time someone specifies type 303 austenitic stainless.
Good luck in welding A286 to anything including itself. We had poor to no luck in welding A286 on many occasions. They make version that is supposed to have better weld ability but again w found it extremely difficult to get a satisfactory weld in place.
If you attempt to weld the material make sure it's in the solution treated condition. Have everything scrupulously clean. The mechanics of welding are fair but it;s the cool down that gets you. Unless someone has come up with something better you have to use a matching filler metal.
