The letter right after the 311 signifies variations in the model. I think the 311H was the last model made but I might have that wrong. About the only way to really date it would be by lumping it into whatever years a certain model designation was made. In your case, you would have to find out what years the 311D was made.
Below is some information I just pulled from shotgun world. As I mentioned, there are those who don't believe this information is accurate for dating a Stevens.
1. Stevens used plain numbers from their first double in 1878 until 1913.
2. Letter prefixes crept in on the serial numbers used on both hammer and hammerless doubles from 1913 to 1939. They always signified a change in mechanical design or manufacturing process which resulted in an interesting variant.
3. From 1940 to 1948 no serial numbers were used on doubles, only capital letters, usually in groups of three or four, the letter(s) sometimes enclosed in a circle, along with an inspector’s symbol ( a heart , a diamond, a spade or some such ‘shape’, on the bottom of the frame behind the hinge pin.
4. From 1948 to 1968 the letter symbols under the frame were changed to a ‘Capital letter with a one or two digit number’ in a 1/4″ circle. This was a date code which you will find illustrated in the Savage-Stevens-Fox pages of your Standard Catalog of Firearms.
5. From October 1968 to March 1988 Savage/Stevens/Fox B doubles are serial numbered in a completely new serial number range beginning at A000001. The six digit (always) numbers, stamped only on the left side of the frame, not on the barrels or fore end or on the wood, are preceded by capital letters from A to E. The letters do not correlate to production years. The letter prefix accompanied the Savage/Stevens/FoxB/Springfield serial number on every gun they made from 1968 on. Beginning about 1978 numbers 1 to 20 were also stamped on the three major components, frame,barrels and fore end iron, to enable the factory to keep 20 guns of like model together in a group for packing in the standard 20 gun shipping carton.
Yours is one of these. Since I am interested only in double guns I stopped looking for numbers on Savage’Stevens doubles after 1988 because that’s the year they shipped their last ‘Stevens Model 311′.
The highest number I have seen was on 20 gauge Stevens Model 311 Series H serial number E957971. The Savage branded imported doubles, over and unders or side by sides, are numbered differently. Each model is numbered in the range created by its manufacturer. As you probably have heard, Savage/Stevens’ production records on their older models were destroyed in a sprinkler accident about 35 years ago, according to officers of the company.
To calculate an approximate number of ‘Stevens Model 311s’ that were made from 1968 to 1988 you could do this math exercise. Since Savage used 5 letters (A to E), each on 999,999 guns, they must have made about 5 million guns. Perhaps 40% were doubles in the various Savage Brands and Private Brands. That makes 2 million doubles of which I estimate 80% were Stevens 311′s. And that’s not counting production before 1968. No wonder the “311″ in its various variations is the all time favorite American made double.
And think how many Stevens 311s ( and Stevens made doubles that looked like Stevens 311s but carried private brands) had already been produced in the years between 1940 (first year of the ‘true’ Stevens Model 311) and 1968, during which time they weren’t serial numbered at all! There must be at least 4 million Stevens Model 311s, in one form or another, out there!
