223 Remington was born in the 1950's as an excellent varmint and coyote cartridge - long before the AR15 came along.
Each state is different. Mass and Maine want you to have a 5rd mag. Some say 10. Alaska doesn't care - if you want a 90rd drum - you use a 90rd drum.
What is important - besides complying with the law - is your choice of bullet. In Alaska the coyote have beautiful, long, luxurious coats and fetch $100+ per pelt. Here you want to use a FMJ to keep the hide damage down - and with a FMJ non expanding bullet, your bullet placement is critical........... or you could spend a long, long time tracking that dogie down.
If you are tagging coyote to remove a pest - then you want a bullet designed to expand really fast. Like a V-Max, Ballistic Tip or a soft nose Blitz style bullet that will tear it up for a one shot kill. Up side to these bullets - if you can calculate the drop correctly - they are still devistating in a 223 Remington at 600 yards.
Most times - you only want 5rd mags. You will have one mag of FMJ's for animals that look nice, One box of cheap Blitz bullets for close in coyotes you wanna blow away, and one mag with nice V-Max type bullets........ and one mag with 69gr MatchKing HPBT for those long hail Mary shots. If these are all full 20 or 30rd mags - they are pretty heavy. You only put 5 in each and use different color tape to tell one from the other. I use red for V-Max and Blitz because all you are gonna see is a fine red mist when the bullet hits. I use blue for the FMJ. And green for the 68gr long distance ammo.
Have a great day