maybe wrong. I think when then Gun Control Act of 68 came into law all guns made after that date were required to have a S/N.I had a old Savage 24 with no S/N. I think handguns always had to have a S/N.
Before 1968, firearms were not required to be serialed, and most lower end guns were not. That, in itself, gives you some information. As the gun isn't serialed. the number "10" is much more likely to be a construction number, not related to just where in the production the gun falls.
Staring at a duece ain't gonna change it to an ace. Your shotgun isn't rare, and there is almost no collector intrest, as others have stated.