Found this too ....
One way to date your Model 1100 shotgun is to locate the code on the left side of the barrel, just forward of the receiver. The first letter indicates the month of production, and the second letter indicates the year of production. By wary, though, as many guns have replacement barrels. [See the 2005 edition number 26,of the Blue Book of Gun Values, page 1,893. ]
Model 1100 serial numbers (on the receiver) started with the number 1001. All but the early guns also have a prefix letter. All Model 1100 Remington shotguns were serial numbered in blocks of numbers. Each serial number has a suffix and the following indicates the meaning:
V = 12ga. standard
2" frame/receiver
M = 12ga. magnum
3" frame/receiver
W= 16ga.
2" frame/receiver
X = 20 ga.
2" frame/receiver
N = 20 ga. magnum
3" frame/receiver
K = 20 ga. lightweight
2" frame/receiver (LW)
K = 20 ga. lightweight
2" frame/receiver (LT)
U = 20 ga. lightweight magnum
3" frame/receiver
J = 28ga.
2" frame/receiver
H = .410
3" frame/receiver