The 5.56 NATO round is a battle-proven round that's been in service for decades - and also the most popular available round for modern sporting rifles. 5.56 rifle ammunition is readily available in small and bulk amounts, accurate, and dependable. Further, rifles chambered in 5.56 NATO will readily accept and fire .223 Remington cartridges just fine, though the inverse is not true - don't shoot 5.56 out of rifles chambered in .223 Remington!
Selecting a rifle chambered in 5.56 can be daunting because of the large number of options, but using the filters (left side of screen for desktop users, "Refine Your Selection" for mobile users) will allow you to narrow down the field by manufacturer, action, barrel length and more. Most modern sporting rifles use a direct impingement gas system, but piston systems are gaining in popularity due to their cleaner-running properties, especially with silencers.
At the end of the day, you'll love any of these rifles - be it a Barrett REC7, Armalite AR15, a Christensen Arms CA15 Recon, or any quality offering we provide.