From Shooting Times
You are, of course saving and scrounging all the .223 brass you can get your hands on. Yes? So,
make your own, right down to the jacketed bullet.
You need your reloading press and a special swaging die. Now gather all the .22 long rifle cases you can so long as they are brass (steel can be used in a pinch and may help with penetration, but it's hard on the tooling and the barrel). Press the spent cases making them into new bullet jackets and fill them with lead! Weight the bullets and load the cases with powder and primer as per your reloading manual(s).
Swaging dies are expensive, to the point one would have to make about 5000 bullets to recover the cost even using "found" lead for the cores. But a man with the right tools can make the appropriate tooling given time and necessity. Something to think on, anyway.