If you buy a top of the line Bushmaster or Colt from the factory set up the way you want it in the 5.56 it will be perfectly on the money. If you spend half as much and get a knock off AR you have no idea about headspace or where the parts came from. Bottom line is step up and spend $1,200 - $1,900 for a top grade weapon.
Our M-4 Bushmaster has matchgrade barrel and trigger and is stamped 5.56 on the barrel and the receiver. .223 in this weapon is not very accurate however when we use Lake City or Federal 109’s in 55 grain FMJ or 62 grain tracers we get a 2 inch group at 200 yards. Again this is what you get when you buy from the factory set up the way you want it.
If you want an off the shelf weapon get an Ak.
I have a couple of Bushy’s and a lefty Stag for my son who is a southpaw. Couple of Armalite’s (AR-10’s) as well. Good weapons all and properly set up.
You’re right about stepping up and buying ia quality weapon of you don’t have any skill/interest in gunsmithing.
I’ve built a couple of AR’s for fun (out of stuff available from various manufacturers) and they were OK weapons but never performed as well as the factory stuff. Converted them to .22LR for plinking.