If you got it new I'd call Mossburg and explain what's going on. Maybe they'll send you a replacement?
If Mossburgs are the only guns you have trouble with, could be the fit. If your not getting in line with the barrel, you won't get a good sight picture. Some guns fit better than others. The other thing I'm thinking is the barrel connection. If that model allows for other barrels to be put on, that barrel may not be turned right on the chamber.
who does'nt build a nest b4 they lay an egg in a public bathroom?
Apparently that guy. ......Only in MD