Yea, sorry about the limited info. but I just recently got this pistol and have never researched guns this much. I have found a new interest for sure, but am just not sure how to determine what it is. The numbers on the butt of the gun match the numbers under the barrel but the numbers under the barrel appear to have a S or 5 in front of them. Too me it looks like 508_ _ _, where the butt of the gun lacks the first digit. The butt of the gun doesn't appear to have any markings showing an attempt to remove the number. I don't know, I will keep researching and hopefully find something. Thanks for the help.