55 grain softpoint for an all around good coyote killin bullet. My all time favorite is the Hornady 52 grain BTHP. Killed a bunch with Hornady 55 grain v-max too but have had several runners with that bullet. Especially on running straight away shots. Expect to shoot twice with any bullet when you're shooting a .223 if you're shooting through a hip and other less than ideal angles. That's another reason I shoot a softpoint or other tougher bullets if I can. At that point I'm trying to hit them good enough to stop them to where I can get a second/better shot on them. You can skin and fix big holes so when things get Western I ain't worried about fur damage. Killing as quickly as possible is my only goal. If you hit one running straight away it's probably gonna spin around. Don't let it catch a second wind. Shoot it again .
55 grain Sierra Blitzking, Winchester Ballistic Silvertip and if you reload the 60 grain Sierra Varminter HP is an awesome bullet for killing power and saving pelts if you want to do that.
I've shot coyotes with 40,45,50,52,53 and 55 grain bullets of several makes and models. They'll all do a good job if you hit one where you're supposed to. Lungs,heart,chest or neck. So I'd say whatever you can find right now except FMJ will get you somewhere if you do your part. I've been shooting mainly softpoints the past few season with good results. Exits the size of a quarter or smaller if you're not hitting guts or the edges of a coyote. They're a little rough on bobcats in my limited experience. I've only shot one in the neck with that bullet and it blew a hole in it on the exit side about the size of a half dollar. So I switch to something I know will be easier on fur if I'm targeting them specifically. Hornady 52 grain BTHP is my go to cat bullet. They're a little more fragile than a coyote. If you can find a bonded bullet shoot coyotes through the shoulder or it'll zip through and they'll run a little ways.
Basically any huntin bullet will do fine. Now really isn't the best time to get real picky about what you shoot.