Probably nothing. The hornet is a cool old rimmed cartridge, that with new powders is very accurate and fun to shoot. Mine uses 13grs of lil Gun so it's inexpensive to shoot. You can load down your .223 to Hornet levels, I suppose, but why. The modern Hornet is very versatile little cartridge. Besides "what's need have to do with it"
The hornet is a cool old rimmed cartridge, that with new powders is very accurate and fun to shoot. Mine uses 13grs of lil Gun so it's inexpensive to shoot. You can load down your .223 to Hornet levels, I suppose, but why. The modern Hornet is very versatile little cartridge. 
