49 is probably pretty close but the circle A where you say it is isn't a date code. Also there should be a number along with the letter for a date code. My 311 made in 57 has a circled A and a circled H on the barrels and the water table where it breaks open. The 5100 was marked Springfield until 48 and the 5100 was dropped in 49. I think with nothing to back it up that the first 311's were made out of 5100 leftover parts thus some carried both the 311 and 5100 designations.
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