Use the right bullets, hit the quarry in the right place. A coyote is no match for a .223 with a Soft Point or HP in the heart lung area, or in the neck/head. Here is a article discussing 223 for deer. Deer are much more resilient then humans so ultimately for defensive purposes it is more than adequate.
““We would agree that there are adequate loads/bullets for humanely taking deer with the .223,” said Tim Brandt, Federal Premium Public Relations Manager. “We have several .223 loads featuring a couple different bullet options that are designed especially for hunting. Our Fusion line is great example. We see excellent weight retention, expansion and penetration from this bullet in the .223 platform. Hunters that live in areas where it’s legal to use this caliber should have no problem finding an effective load to take into the deer stand.”
Tim also included the following test data, which shows that the average Fusion bullet penetrated nearly 15 inches of gelatin and expanded to .54 caliber. Most of a bullet’s expansion happens within the first inch or so of penetration which means that the Fusion load effectively sends a .54 caliber ball through the vitals of its intended target. I observed recent tests of the DoubleTap load with similar results.”