Here are some links with pictures so you can determine what happened to your piston. Two Stroke Piston Diagnosis Piston Failure Analysis I also attached one that includes pics of the cylinder and piston. Defininitve Dave posted this one on the OPE forum. Kyle Mulligan, I believe I mentioned these in a thread of yours when you were working on a MS260. I just got around to digging them up.
Another great FFHCMM..... that's Fine FHC Member Moment..... Always looking out to lend a hand.....priceless.
Does this picture appear to be early stage bearing failure, I debated about that or too lean a fuel mix? I suspect a tear down and assess is in the near future. It's on an Sthil 066 I bought cheap.