When I copied and pasted the chart off the Ruger site to the forum, it jumbled all the numbers together

. I looked up your number you posted and starting in 1956, the serial # of the first gun was 31857. By 1957, the number was in the 50,000 range.
So your gun was likely from 1956.
Does that fit with the history of the gun you know from your relative?
Incidentally the serial numbers were not always assigned in exact sequential order. Therefore the number does not correlate with the number of guns made in a specific year.
Does that fit with the history of the gun you know from your relative?
You can also contact Ruger directly at Telephone: 603-865-2424. If you give them the full serial number they can give you the exact date of manufacture.