I just wish they could print .22 Long rifle rounds!
I don't think we will see that happen but there are propellants that can be manufactured from household chemicals. You won't get the velocity of powder but you will get enough to be deadly at close range. If the propellant is stored as part of the weapon, it could be metered on an as-needed basis. I think we are going to see a lot of innovation in the production of printed weapons, including the ammo.