^^^this^^^ do you reload? There are lots of good calibers for the ar platform. But the majority are fairly hard to find ammo wise (if not damn near impossible in some places) and can get pretty expensive if you shoot a lot. Reloading is the only way to go with most of these. My fave rounds in the ar platform (other than 223/5.56 which is still my fave) is the 5.45x39 rnd because its cheap as *s-word, accurate, and all the milsurp ammo is steel core. Zaps sweet little holes in everything! Haha!! Just dont swiss cheese your friends steel targets, they get all butthurt about it. Hahaha!! Other fave is the 450 bushmaster, cause its a thumper! I shoot prolly 30,000-40,000rnds of 223/5.56 a year and it is still my fave
But my "suggestion" would be to stick with 223/5.56 and build (or buy) a new upper for some better accuracy. I have set up a bunch of them in many many lengths and barrel diameters. From 7" pistol barrels to 29" waaayyy too expensive barrels, and from thin light carbon fiber pencil barrels to fatty 1.25" bull barrels. And literally everything in between. Haha! Time and time again the most consistent dead nuts accurate setup is a chrome lined 18"x1" 1in16 twist fluted bull barrel drilled for midlength gas system, on a billet upper, with a carbon fiber freefloat handguard, and one of the smallest low profile gas blocks available. Then use quality 62-72gr ammo and you will quickly become bored with the ar platform because it is soo accurate, its almost not fun anymore. Haha! I have built 8 different uppers in this same way with various different aftermarket brands for parts and they consistently outshoot much longer and much more expensive "match" grade uppers. Every time i build myself one, i let a friend shoot it and they freak out and have to have it. Soo then i make myself another one... ha! With all of them so far ya can stack a 30rnd mag on a golf ball at 100yrds literally as fast as your finger can pull the trigger. And also the same on a clay pigeon at 300yrds. Taking your time its not hard at all to put multiple shots thru one hole, make smiley faces, write your name, etc.. I am currently without one but just ordered a new barrel the other day to start another one. Lucky number 9!! Maybe ill keep this one!!!