The other issue could be that you simply don't have enough ammo in your inventory to ship. Remember that we have to ship out factory boxes of 20 or 50 rounds per caliber. If you have 12.1 rounds for example that won't ship and will simply stay in your inventory until a future order adds more ammo and you have at least a factory box's worth of ammo to ship.
Another issue is that you put in your shipping request BEFORE you had ammo in your inventory. If you do that our system will void your request. If you request ammo you don't have allocated yet we obviously can't ship it.
In summary: you need to have ammo in your inventory in order for us to ship AND you need to tell us you want it shipped.