The 870 came out in 1950 to replace the Model 31, it was much cheaper to make. Never owned one, but I do own a 1948 31 TG, which many consider one of the nicest pump shotguns made
"Those that think they know everything are annoying those of us that have Google." - Dr. D. Edward Wilkinson
Note to self: Never ask an old Fogey how he is doing today. Revised note to self: Keep it short when someone asks how I am doing.