My 870 has "Remington 870 Magnum" on the left side of the reciever and "Special Purpose" on the right (ejection port) side of the reciever. I bought the gun used and it came with a vent rib, rem choke 26 inch barrel. From what I have researched it is from around 1985 (maybe wrong here). My question is what is different about it compared to 870's that have "Express Magnum" on the reciever. Do I have an older model with non MIM extractor, metal trigger quard assembly, etc? Also, what, if anything, does special purpose designate? (crappy cell phone pic with 18.5" barrel on) Thanks for any information guys!