Call Mossberg Customer Service right away, they have excellent Customer Service. Also check their website for authorized warranty service dealers in your area, they may be able to exchange the barrel on the spot and take care of the problem barrel with Mossberg, or fix you up with a taller front sight. That will also save you the shipping and time.
I have dealt with alot of gun manufacturer's Customer Service's, Mossberg has always been outstanding. They will take care of you, just try to get them to swap it at one of their warranty service dealers if there is one close by. They don't have to do that, but may if you request it due to deer season being so close.
Their slug barrels are some of the best. Sorry you have a problem with yours.