I use a 7mm mag fl sizer as a shoulder "bump die" and neck sizer. It has body clearance so it won't size the case and is too short anyway. I get several firings before they start to stick above the belt and just bought the collet die sizer from larrywillis dot com. That collet works slick but you can size the body diameter down too far if you run the die down tight to the shell holder. I set it to just bump the area above the belt.
If you want to size the brass back to factory at the belt and not pay for the willis collet you can part off a std 7stw full length sizer at the shoulder then turn about .050 off the base so it'll get to the belt before it hits the shell holder. Parting off produced a few sparks but turning back the ends and chamfering, it cut like butter.