The best 5.56 Ammo?

Black Hill 62 Grain & Speer 75 grain Gold Dot rounds are heavy bullets and immediate expansion-  nickel-plated brass reduces malfunctions and guarantee reliable feeding in your self-defense carbine.

Some good Long Distance Any 77grain boat tail hollowpoints. Winchester is fine. 

Hornady Superperformance. The boys and I can obliterate a melon from way over 200 yards 

 Purchase with what will ensure Safety in the home (not hit anything besides bad guys.) Expansion is an element to review. Expansion is crucial for stopping power and minimizing collateral damage. A well-expanding round increases wound size and reduces the chance of overpenetration. The degree of expansion depends on the projectile’s velocity and composition. For instance, a harder expanding bullet, like copper, starts deforming at around 2,000 fps and expands more quickly than a softer bullet, which begins deforming at approximately 1,600 fps..  Overpenetration is a common concern, right ammo can mitigate this risk.  

Also, what you rifle if twist rate is? Brass casings are generally more reliable and gentler on your rifle than steel casings

Some good Options: (Factory Ammo) 

Hornady Critical Defense 55gr

Speer Gold Dot 62 gr 

Winchester Defender

Can you use .223 ammo with 5.56 chamber?

Yes, you can shoot .223 from a 5.56 chamber without any issues. The 5.56 chamber is built to handle higher pressure and has a longer throat.  Don’t do the reverse firing 5.56 in a .223 chamber. If you’ve got a .223 Wylde chamber, it’s designed for both.