highestangel, mine is in the 500 serial range. i looked at 2 when i bought mine, 1 had a deep distinct F stamped in the bottom of the reciever, mine has a tiney F stenciled, need a magnifying glass to see it. i assume it's been "fixed". havent' looked at the pin yet, though. finally quit raining, after 3 days, i'll try to get out and test it a little more real soon.