how can you tell the year of manufacturing with no serial number / has markings on barrel 00 and two stamps that look like a duck head from left to right with a small circle and the letter p inside above it / other marking on right side of barrel is the big oval circle with a big S that has a letter p inside the top of the S and a letter t inside the bottom of the S with a small s stamped on its side to the left of big S /also the 00 and two duck heads on the reciever side lower left