took them to work measured them with digi calipers the "shelf" was 81.5 around the ringlands it wasd like 81 mm or so is this normal

 

Yes. Pistons smaller around the lands and crown to allow for expansion. Measure 0.500" off the bottom of the skirt and it should be close to 81.50mm.

81.50mm pistons generally means that the piston is meant to run in a 81.500mm bore and has the clearance "built-in" to the skirt by being saying 0.0035 smaller.