It's unlikely that your gun was from the forties, at least not the early forties. One of my skeet 20's was shipped in 1948, is pre diamond checkering, and is serial number 14,527. You should get your gun lettered to confirm the date. I didn't know anyone dares to create a date chart for 21s. It can't be done. I suspect the diamond checkering may be original and your gun is actually from the fifties.