I am very new to firearms collecting, but am very interested and really need some help. My understanding is there is an original Sporter II model 6500 with SN pre-fixes of SP, then there is the AR-15A2 Sporter II rifle with fixed stock and 20 inch barrel, then there is the AR-15A2 Carbine with collapsible stock, 16 inch barrel, and shortened forearm, then I won't even talk about the Tactical Carbine, Government Model, etc. The question is I have what I believe to be a pre-ban AR-15A2 marked Sporter II with an SP serial number, collapsible stock, short barrel, shortened forearm, flash hider, and bayonnet lug, so what gun do I really have, what is the model number, and what is it worth? Thank you.

I don't know what it is worth, but it sounds nice.