Stevens 311 acquisition

Just picked up a clean Stevens 311 in 12 Ga. I think it is a 1947 or 48.  It has a lettered date code of D H and a circled D and a Tenite stock. Case coloring is good and it only been fired a couple of times. I have been trying to figure out what it is choked. I don't have a bore choke gauge. Each barrel is marked on the underneath with a M. Does that indicate that both barrels are Modified?
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I have a 311 in 12ga, well, the Sears version anyway. In fact, just ordered a few parts for it yesterday.

Would agree the "M" on both barrels indicates modified choke, I'll pull mine out later today and confirm.

Is your Sears model from the 40's? I have read that they were putting asterisks to indicate choke on some models and that the date code style changed in 1949. Mine has no asterisks and only lettered date code. I have never seen a specific date code chart for the 40-48 span but am pretty confident mine has to be 47-48 since it also has the Tenite stocks. Mine also has the 5100 frame but does not have the Stevens bird dog engraving.
I attempted to get a measurement of bore with a caliper but it is difficult to be real accurate with the knife edge. It seemed like I was more in the full choke range but I need to find my spring loaded inside divider to get a better measurement.
Does yours have the Tenite stock?

Mine is '64 with wood forearm and buttstock.

I forgot to mention that mine has 30 inch barrels with 2 3/4 chambers. What is the word on lengthening to 3 inch chambers?

Mine is a Sears (Eastern Arms) 16 GA with a Tenite stock. No indication of DOM or choke, so no help there. I’ve installed the Wolff spring kit and had the forcing cones tapered. A good gunsmith could tell you if the barrels are meaty enough for a chamber lengthening. Mine holds it’s own on the sporting clays course, and I wouldn’t part with it for the world. Good find!

Oh, and patterning is the best way to determine actual choke, dimensions be damned.

I agree that patterning is the way to tell how well it shoots to point of aim and measuring shot density. I will have a gunsmith check it for wall thickness and choke bore. If it is full/full then I may explore putting tubes in. If both bores are modified I may leave it alone. If it is full/mod maybe I would have one tube put in. I don't want to fire it until I can get the stocks replaced with wood. My Tenite stocks are in great shape and still have original stickers on them and don't want to risk cracking them.

The most important thing with Tenite of that vintage is to keep it out of sunlight. It’s very susceptible to UV degradation. It was a favorite for overmolding steering wheels, but if you’ve ever seen an old car with a cracked plastic steering wheel, that’s why. Especially convertibles and Jeeps.

I finally got around to measuring the bore. The right is .702 and the left is .698. That puts it in the range of Mod/Mod. I will probably skip putting in tubes but am going to swap out the stocks. I may get the chamber extended if possible but will wait until I shoot it first.