Hey Speedchaser how can I duplicate the piston texture seen on the piston in the pic?

That is a picture of a ROTAX piston out of a sled I found on the web I have no idea if its a factory texture or after market assume its a OEM piston at this point anyways what kind of cutter do I need to perform this I know the pistons are made from some really hard stuff, it almost looks like a square groove to me but I want the bottom of the square groove to have a radius so it wont promote cracking but still a reservoir to hold oil for better lubrication.

Piston also appears to have been coated with a anti scuff coating found on many OEM pistons to get them out of warranty when the owners don't allow the proper break in and or warm up time.