If you can find a piece of pipe, that is a few inches longer than the complete round, that the case will fit inside of, but the rim will still rest on the end of the pipe, you can use the inertia method to get the weight of the projectile to help it out of the case. you turn the round upside down, and insert it into the case with the rim resting on the end of the pipe. Raise both pieces a few inches of the ground, and slam the bottom end down on a hard surface. It might take a few hits to inertia the projo out. remove the fuze and put some padding on the tip of the projectile before you do that, so that when it pops out of the case, the padding will catch it from impacting on the hard surface. If you can't find a close fit of pipe, make a close fitting ring of wood that supports the case rim, and use a bit larger diameter pipe.
you can also squirt some penetrating oil into the case through the primer hole, with the round pointing down. the oil will seep between the case mouth and the projo exterior to reduce the friction during the inertia impacting.