Why would you want 2 rifles of the same cartridge??

I fully understand why you would want that. I have several 223's and more 30-06's than Icare to count.

If you want another 223 and you think you would shoot it more because of ammo cost, then I would buy another 223 in a heart beat. Heck I would recommend buying 4 or 5 of them if you want to!! However a different configuration or action type might be fun. And the idea of an AR is also a great idea. Tom.