Large displacement (generally anything 250cc or above has problems with two-stroke forged pistons collapsing. 

Wiseco and Wossner seem to be the worst with the collapsing problem.  Record the measurements on a new LT 250/500, KX 250/500, CR 250/500 , etc. piston with the correct clearance and run it for a weekend.  Take the pistons out after a weekend of racing or hard running and measure it and compare the dimension to the dimensions of the new pistons. 

You will usually find that where the largest diameter was on the new piston's lower thrust sides of the skirt is .003" to .007" smaller than it was when it was new.  You will usually find that where the smallest diameter was on the new piston (just below the wrist pin and parallel to the wrist pin) is now .003" to .007" larger than it was when it was new. 

The conventional piston design that the forged piston manufacturers are using does nothing to prevent the collapsing problem.  The cast piston's alloy is hard enough that is much more resistant to bending (collapsing) but is too brittle and weak for the conventional cast design for the load they are experiencing in the high RPM modified engines.

We do not have much choice at this time but to use the soft collapsing forged pistons in the big-bore long-stroke single cylinder two strokes.

A forged Wiseco piston will run for some time before the cracks will propagate to the point where a skirt will break off and turn your engine to junk.   

A severely over stressed cast piston may not go very many engine revolutions from the time a crack starts until the piston breaks into many pieces.