I have 2 870's. One is a 3 1/2". The other is quite a bit older, and I believe the barrel is chambered for a 3", but I'm not sure. I don't have a 3" headspace gauge, but I can put a 3 1/2" shell in with no reistance. On the barrel it says, : "Use 2 3/4 or 3" Shells in Magnum Receivers. Use only 2 3/4" in all others." There is no difference in a 3" and 2 3/4" receiver. Is it safe to fire 3" shells in this shotgun?

JD
You can shoot 23/4 abd 3" shells in a 3" chamber.
A 31/2 inch shell will go in a 3" chamber but do not fire it. When the crimp opens up it will open in the forcing cone and cause very high pressures.
George

If the last digit of your serial number is an "M", you've got a magnum action. If you still aren't sure about shooting 3's in it, take it to a gunsmith and have them check it out.

George, sure I wouldn't shoot the 3 1/2 in it; it wouldn't feed or eject anyway because the loading port is too short. I just wanted to know if you could put a 3 1/2 in a 3" chamber but not a 2 3/4".