hypothetical question

[Olle]

Originally Posted by CavScoutEurope

If made before 1968 (?) it is legal not to have a serial number on the firearm.

Does this go for all calibers and types of firearms? I have a .22 rifle without serial number, a single shot cheapo my father-in-law bought at Sears in the 50's or 60's. This was obviously legal enough back then, but I have seen comments saying that it was only .22s that could be sold without serial numbers.