Serial numbers were required on firearms prior to the 68GCA,,but not on 22rf cal long guns,,nor on shotguns.
The 68 law required from that point forward (12/68 I believe) that those two types also be serial numbered by their manufacturer.
Others had been required to be serial numbered prior to the 68 law.
That law only added the last two types that had been up to that point ser#'d optionally by their mfg'r.
Some mgf'r's did already ser# their 22rf cal long guns and shotguns. Some did not.
Some ser#'d some of the models in their production, but left other models unser#'d. Winchester is a prime example.
The Fox Model B is actually made by Savage. It's a cosmeticly altered Stevens 311.
Savage owns both the AH Fox name and the Stevens name having bought both companys out in the '20's. Savage used the names to their marketing advantage over the years.
AH Fox before being bought out by Savage serial numbered all production,,even the flare pistols made for WW1 contract.
Savage/Stevens/Fox Co. is another that ser#'d some production, but failed to do others in their line.
Then there's the ever present unserial numbered example that shows up in later production. Factory mistakes do happen sometimes as much as they do not wan to admit it. Also firearms make their way out the facilitys as parts to be assembled later.
The as-issued Mosin Nagants don't even have a legal ser# by US standards. The ser# placed on them in original manufacture is actually up on the bbl, not on the receiver. Not sure about the N/E Westinghouse made rifles.
In many other parts of the world the bbl is the 'firearm' or controlled part as the frame is in the USA.
No one ever payed much attention to the matter, what with the rifles selling for $10 and under.
Then came the 1986 upgrading to the GCA with the importation being allowed once more of Milsurp firearms.
A flood of M/Nagants came and still do it seems.
That '86 law required the 'import markings' on the firearm and notice was taken of the ser# placement or lack of it on them.
For that reason, most all of the post '86 M/N imports have either the bbl ser# restamped onto the recv'r by the imported before sale, some more discretely than others.
Or more recently a new serial number assigned to it and it and the import marking info bill board marked on the left side of the recv'r.
Duplicate ser#'s do happen during production. Sometimes the stamping process was done with individual single digit stamps. Some used a self indexing stamp on a roll die type assembly. Either could cause a duplicate.
Most mfg's had a way to deal with it. Some by adding a simple odd letter prefix or suffix to one of the dups.
IIRC Ruger used to use a cap X as a suffix on a serial number. It of course changes the duplicate to a new number,,it also lets a collector know that the gun was originally a duplicate #'d gun. For that some seem willing to pay a bit more.
