[killdee]

I have been reading a lot on here and elsewhere, trying to figure out the age of this 20 gauge. Its a Topper M48 se#4873 no letter prefix or letter below Harrington And Richardson on the receiver. Any ideas on the MFG, date?
Thanks, Killdee

 

[killdee]

Since theres no letter prefix, would it be from the first run in 1945?