You could probably figure it out in reverse by looking at the components and comparing those to the various model descriptions, but I have had trouble myself finding an all-inclusive list that describes the features of each model.
Some of the model distinctions are pretty subtle (eg. 11715 vs 11721 is just night sights vs regular sights). Maybe start by posting a picture...? Some of the experienced people here could probably nail it down pretty quickly with a few key questions after that.