Magnum blocks

Both Blueprint and ATK stoker motors (long and short blocks) all show being .040” over Magnum block based. I’ve always wondered why they all bore to .040” as a standard instead of the typical .030” I can’t see used Magnum block cores being that bad as to need .040” to clean up. Maybe they get better pricing on the KB or Icon pistons in .040”? I don’t recall ever reading anywhere in their literature that the blocks are sonic checked either. Who really knows what is a magnum blocks overbore limit?