For shotguns with removeable barrels, the code will be valid for the manufacture of the barrel; maybe for the receiver, as barrels do get switched around.
Month Codes: [first letter]B - L - A - C - K - P - O - W - D - E - R - X1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12Year:______Code: [second (and third*) letters]1960_______ G1961_______ H1962_______ J1963_______ K1964_______ L1965_______ M1966_______ N1967_______ P1968_______ R1969_______ S1970_______ T1971_______ U1972_______ W1973_______ X1974_______ Y1975_______ Z1976_______ I1977_______ O1978_______ Q1979_______ V1980_______ A1981_______ B1982_______ C1983_______ D1984_______ E1985_______ F1986_______ G1987_______ H1988_______ I1989_______ J1990_______ K1991_______ L1992_______ M1993_______ N1994_______ O1995_______ P1996_______ Q1997_______ R1998_______ S1999_______ T2000_______ U2001_______ W2002_______ XAs maybe seen, the year code letters duplicate; some knowledge of when the model was introduced should resolve the actual year of manufacture.
Call Remington and give them the serial number, they will tell you when it was born, however keep in mind they due make errors. So, anyway, according to the above info, my PA barrel code and lack of serial # prefix, my Wingmaster has a mfg date of June 1953.
Back up what they tell you with this information; DECODING REMINGTON SERIAL NUMBERSModel 870 LETTER PREFIX1950 TO APPROX 1968: NO SERIAL NUMBER PREFIX1968 TO PRESENT: LETTERS USED (IN SEQUENCE)S-68, T-74, V-78, W-84, X-90, A-91, B-94, C-97, D-01, AB-05Model 870 LETTER SUFFIX (DESIGNATES GAUGE)V 12 GA. What is the barrel code and the serial # letter prefix?
I have contacted Remington and they confirmed that information above is correct.
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**The first letter on your barrel is the month your firearm was manufactured; the second letter is the year it was manufactured.
I am assuming your second letter in the barrel code is "Q" based on what you say above 1978 or 1996.
If it is a 1978 then the prefix letter in the serial number on the receiver will most likely be "V".