This my first post so please bear with me. My new 60-pro has a number stamped on the cylinder yoke (I think it's called) and I was curious about it's meaning. I know about the model number (mine is a 60-15) but this is different - see photo.
Looks like 457 to me, LOL. Seriously, it probably is just a new way of stamping an assembly number. If the same number is stamped inside the sideplate or under ths left stock that's what it is.