From JR Lawrence-Wow, I don't even like the AR-15: personally I think it is a stupid weapon. A 308, 30-06, 6.5 or a 243 would be a better choice. But, I get it: the AR-15 sells, because it has a cool look - that is why the liberals hate it. But a 243 would reach out much further with less noise, less kick, closer groups and cheaper ammo. You don't need a cannon to do the job. A 30-06 or a 308 (M-14) can center a group on an 8" bull's eye at 1000 yards with open sights. A 243 can do that, with more drop. A scope makes it easier.
I am non-plussed by this - you have familiarity with firearms - BUT - currently - 20 rounds of .223 run $5 versus 20 rounds of .243 run about $15 - rounded down. The AR-15- ,223/.556 is not a "cannon" - it was developed for lighter rounds to carry more ammo by troops using the M-16.
As far as noise, kick, grouping - comparable in many ways - including the range of bullet weight- about 55- 75 Gr. Grouping - depends on the weapon and shooter.
The .243 is a larger round and carries more energy at muzzle than a .223.
Apologis - a bit off topic.
It is fine that you do not care for the AR-15- America's most popular rifle. I do not own one, but use Ruger Mini-14's and HK -93 rifles in .556.
Anyone that can center an 8" group at 1000 yards with open sights is a far better marksman and better eyesight than I - I cannot see an 8" target at 1000 yards. 100 yards - give you that.
Given that a .556 is not generally considered a deer rifle, and a .243 is often used for deer hunting. Due to the increased round energy.