I have been doing something similar with full bore ammunition using the Frenchmethod of making gallery ammunition, using flash paper for propellent and a lead ball projectile.. I have managed to source proper flash paper from a Magic Supplies company and cut them into 1/2" x 1 1/2 " rectangles, folded into a W and put in the case. The projectiles are simply lead balls of the appropriate diameter (basically bore diameter plus a few thou) coated with liquid Alox. I am using .312 for .303 and 7.62x54 and .324 for 7.92x54, 7.92 Kurtz and 8x50 Lebel. You just need to press the ball into the mouth of the case with thumb pressure.. no need for a press. I believe buckshot will work with .308, but you need to check..
They are perfectly usable on a .22RF range and are extremely accurate. There is no danger of detonation, over charging or use of wads etc.. The bore is a bit mucky afterwards, but this is mostly from the Alox..
The method works well for rifle calibres up to about 8mm.. above this there is a tendency for the ball to stick in the bore.