Buy a new one, under $25.
Get one with plastic container/hammer and an aluminum handle. Before using it, wrap the plastic around the metal handle with heavy duty tape, such as hockey tape or electrical tape.
Next, make sure you have a very solid surface to whack it on. If the surface is soft, such as plywood, then you have to hit harder and more often to remove some bullets. I use a lead block or the top of my work bench, which is 5mm steel, over 2 inch thick Fir planks.
If you insist on using wood or nothing else is available, build a block, so that you can pound against the ends, rather than the sides. Less give. Less broken hammers.