Kyle, the main difference is 5.56 has a higher chamber pressure than 223. The 5.56 NATO pressure is about 58,000 psi and the 223 round is approximately 55,000 psi. Doesn't sound like a huge difference but when firing a 5.56 round in a .223 chambered rifle due to the longer throat on the NATO chamber, you’ll reach pressures of 65,000 psi or higher. That's why it's it's not safe to fire 5.56 in a rifle chambered for 223 but you can shoot 223 threw a rifle chambered in 5.56 all day long. Due to the higher chamber pressure 5.56 is a little more effective than 223. What makes deciding if ones better than the other is 223 has become the standard for civilians so manufacturers put more time and effort into making better rounds for 223. While 5.56 has a higher chamber pressure 223 has better bullet designs wich helps with expansion, plus it's a little bit cheaper to buy. Personally I really don't use 5.56 because it's easier to find match/defense rounds in 223 and it's cheaper. Think since 223 has more options it makes up for the few thousand psi less than 5.56. hope this helps.

Kyle, the two biggest differences is the pressure (5.56 is higher) and the throat length. The 5.56 also has a longer throat with a difference of . 125 inches in length when compared with that of the 223 Remington bullet. The longer throat allows more holding capacity for gun powder in the 5.56, thus implying that it has a higher performance as compared to the 223 Remington (5.56 should not be fired in a .223 stamped barrel). This in term brings barrel specifications into play on the accuracy front. .223 is generally more accurate in a .223 chamber and 5.56 is generally more accurate in a 5.56 chamber because of corresponding throat size. This can be thought of as the length or distance the bullet has to "jump" to engage the rifling. The Wylde Barrel splits the difference in chamber size and should technically be equally accurate with both .223 and 5.56. Also the twist rate plays a factor in bullet weight stabilization which is touched on here : idahostatejournal.com/outdoors/xtreme/understanding-twist-rates-on-ar-15s/article_88f06b3e-57de-5c58-b273-7fff0476ed33.html --------------- Cheers and stay safe!