As others have posted, you can fly with up to 11 lbs. in factory boxes in your checked baggage with most airlines.
Tell them you have ammo.
Should work out to about 5 boxes of one ounce 2 1/2" shells although I'm sure you could get away with 6. I have flown from Salt Lake to Calgary with a flat of shells that I split between two checked bags but that may be risky. More than likely, they will not weigh the boxes...