If you're into reloading and are trying to keep your logistics under control, the .243 can be reloaded by necking down the .308 cartridges you already own. Once-fired military brass should do just fine (or so my sources tell me, I haven't personally done it).
The runner up is the .223; a light sporting rifle in this caliber would be good on coyote-size game. I personally hunt with my AR-15 HBAR sporter for Javelina (legal here in Arizona with a 5-round magazine). Something like this would then give you a back-up or secondary fighting weapon, in addition to hunting applications.
Hmmmm, maybe you need TWO more rifles.
