What the heck are you thinking??? That is one of the dumbest ideas I have ever heard. Yeah you could probably do it, but why would you? Thats like Cutting a load of fire wood with a rock. Could get it done, but it is not right. No matter how you look at it, the 223 is the wrong choice for any animal bigger than a medium sized white tail andf it is debatable at best for that. No matter how fast it goes, etc. it doesnot have the power to effectively and consistently take elk. If your under 50 yards and a perfect shot maybe, but even there a bow seems a better choice. The point of a bullet of rifle is to cause death by shock, meaning power. The 223 will never pack enough power for it. I have seen rounds from a 30-06 lodge in the front shoulder oa and elk at 200 yards and never make it into chest. Do that with a 223 all you will do is kill the elk in a few months from infection. The larger caliber guns will atleast cause enought trama to slow an elk, a 223 wont. The energy alon is not enough to make it through the body.
You will also be really mad when that 400 plus bull is out there at 200 yards and you cant even make him flinch. Bottom line is elk are tuff sturdy animals and a 223 is an injust way to hunt them.