I wouldnt know where to start,alot of info has already been uncovered here in previous replies.
I've always been a .308 or large bore weapon shooter, just this past year I've read up on the 223/556 & decided to make it my primary SHTF rifle & carbin.
I alway thought of this caliber as a pea shooter,but its about bullet choice, also shot placement, even a wounded can prove to be more effective, it will take one or two people to carry this wounded person.
I love the M4 carbin,it is plenty accurate enough,but decided to also try my hands with a 20" heavy barrel
Im no expert on scopes,but wanted a decent varmint scope, that could also be used a s aspotting scope,so I went with a 6X24X42,Aimpoint on my carbin has served its purpose nicely.
Here a few old pix of my set up,have added a ARMS40 rear sight on the carbin,flip ups and kill flash on the scope since pix was taking.
Bushmaster 20" ,found out a mil-dot master works great with a little practice.
M4gery
I sighted my rifles in , using SS109,use alot of wolf ammo for plinking and trigger time.
TG