[pavel22]

Because synthetic lubricants don't allow much wear on rings that is the reason for using good hydrocarbon oils during breakin, or about 1000 miles to wear the ring edges in nice and smooth.. The corners of the rings have to wear nice and rounded or tapered to hold that tiny crevice of oil between the ring and cylinder walls for minimum friction. In fact it has been known that many NASCAR engines used rings that had been machined with those rounded or tapered corners (wanna start an argument with top engine builders, advocate one) to shorten breakin and improve power. Any nicks or chips in those rings cost power and chips and nicks are what you see on those engines taken to rpm limits under load right away.