I've become interested recently in the 300 Whisper which is basically a 221 Fireball necked up and fire formed to a 30 caliber. It can be loaded subsonic and can be quite accurate, supressed and powerful with it's large 30 cal, 220 grn bullet leaving the muzzle @ 1070 fps or less. It can also function through an AR-15 mag. Fascinating. So, does anyone have a list or knowledge of wildcat cartridges that begin life with the 223 cartridge case. Just curious.