Now that I have completely discouraged you, let me point out that the .223 WSSM has the potential to be the best coyote cartridge available in an AR.
I said before that I think the best rifle for coyote hunting is the AR-15. But the best cartridge is something else. I much prefer a .22-250 Remington or a .220 Swift, which for the most part are not AR-15 cartridges. While at least one company, Olympic Arms, is offering a .22-250 in an AR, the lower has to be modified, so you cannot just use your gun and add the upper. But they also make ARs in .223 WSSM. Factory loads drive a 55-grain Ballistic Silvertip bullet at 3850 fps. If you handload, it can move a 50-grain bullet well over 4000 fps. Those are serious coyote hunting ballistics that will stomp them flat where they stand.
Ammo is offered by Alexander Arms, Hornady and Wolf, so availability is not an issue. Hornady has a 123-grain A-Max bullet that moves at 2620 fps. I have shot some coyotes with this load and it killed them just fine in spite of the bullet being designed for targets and not hunting. Bill Alexander says he has had the best luck on coyotes with his ammo using a 100-grain Berger bullet around 2800 fps. Handloaders can push a 90-grain Speer TNT bullet close to 2900 fps.
As far as I can tell, there are currently four different chamber designs for the 6.8 SPC. But this is subject to change because of a never-ending quest to make this cartridge perform beyond the rules of physics.
Many of the reported results on the Web and other places are from loads that exceed safe SAAMI-accepted pressure standards. I’ll limit my discussion here to the SAAMI-accepted chambering and the mainstream ammo products that are loaded to the accepted pressure standards.
The 6.8 SPC was designed to bring a bit more hitting power to the AR-15 for military applications, but the government took a pass. It lives on as a hunting and self-defense cartridge. It uses a .270-caliber bullet, which is probably right on the tipping point between predator cartridges and big-game cartridges.
The Hornady load with a 110-grain V-Max bullet has an MV of 2550 fps from a 16-inch barrel. The few coyotes I have shot with this load played by the rules and politely fell. While my experience with the 6.8 on predators is limited compared to some of the other cartridges, I think this would be a good choice, particularly for hunters looking for a dual-use cartridge.
Predator hunters were using ARs long before it became “cool,” and I suspect that with the ever-expanding cartridge and ammo options they will be using it well after the fad has faded. With the right cartridge it’s simply the best choice.