Weatherman,
I don't know whether you bought this rifle new or used, but I can tell you that the tight chamber problem is not going to get any better, is not going to resolve itself, and could be highly dangerous if you have a short chamber, rough chamber, or headspace issue. If new, send it back to Mossberg immediately and tell them to fix it. If not, get it to a qualified rifle smith, who can check headspace and ream or polish the chamber correctly.
My wife once had this exact problem with a brand new Remington 700 Classic, and it had to go back to Remington.
Best, Mannyrock