Hi, just took apart my 870 12g for the first time, I just took apart my 870 20g last week though! Everything is back together. Only trouble is, the lever gate? doesn't go up all the way? and I have having trouble loading rounds in the tube for HD. I cocked the gun and the gate went had better results. This shouldn't happen. I dry fired it and it's having problems still. 
It looks like the lever gate is exposed OUTSIDE of the gun, not flush with it or inside the gun, its poking out. On my 20g it's flush!
It looks like the lever gate is exposed OUTSIDE of the gun, not flush with it or inside the gun, its poking out. On my 20g it's flush!
Thus making a gap so the lever gate couldn't go up a 1/4 of a inch to fit the round in the magazine tube. 