870 suger mag port cover problem

[bdd9484]

I was shooting my 870 express super mag the other day to test it out for goose season. I shot a 3.5 inch shell through it and when I tried to eject the shell it jammed. When I inspected the gun, I noticed the port cover on the bolt was damaged. The top channel of the cover was crimped, making it unable to retract the whole way. It is easy enough for me to buy a new cover, but I would like to know what went wrong. Is it normal for this to happen from time to time? Did I do something to screw it up? Or, is this a symptom of a much larger problem with my gun? Can anybody help me out?

[Synchronizor]

I don't have a lot of experience with the SuperMag 870s. I'm not a fan of the 3.5" 12ga shotshell in general, and I think it was kind of a stretch to try to shoehorn it into the 870's 2.75" frame. However, I have heard from others that the port cover is a weak point in the SuperMags, and that it can sometimes have issues under heavy recoil. It could also just be a defect, or the result of improper disassembly/assembly.

Is this a new gun?