Well no, because the engine, like the round, is the bit that contains the explosion. The fuel is the powder. To answer your question about how does a bullet function without powder, you could say it's fired electromagnetically like in a railgun, but then you'd say that 3D printers can't print electricity. Blue160 would make the car analogy again, only in relation to electric cars and flat batteries. You will make the claim that it is an electric car without a battery, I will point out that technically a 3D printer can print a battery shell, what it can't do is print electrolyte's (though metal printing can get you your coils and things).