With regards to the Bullet Shape, that is only actually a benefit is you expect to impart an axial spin on the slug, as the rifling inside a gun barrel would do. It doesnt sound like you expect to have that kind of control at the launch (though it could be theoretically possible with well timed magnets or some such).
Without that spin the bullet will inevitably start to tumble, which will hurt accuracy quite a bit even in space (rotating systems can skew the trajectory, not unlike a curve ball). Without that spin, a sphere is far more efficient. Specifically, a sphere with golf-ball style divets. Believe it or not, the divets actually decrease that drag forces from the atmosphere, which increases range. In this case that would decrease the force required to make orbit.