me and my dad between us own 3 870's. only had a problem one time. dad was turkey hunting, and shot a shell that would eject. he took it apart, and the sheel had expanded, and got caught. It wasnt the gun it was the sheel. It was a 3" federal turkey load. he said hell never shoot them again. Your main problem is the fact that you bought a super magnum. There is no need for the 3 1/2" shell. The toughest loads out there in 3" will do the same job as the 3 1/2" with less recoil, and noise. My dad has the super magnum, and he just bought it for the synthetic stock, because the regular 870 doesnt come in synthetic. He only shot3 1/2" shells when he first got it. Since then he has just shot 3". They are cheaper, and are easier to shoot.
Do yourself a favor, and get the 870. You will never look at shotguns the same way again.