yes the S&W M&P 15 sport II in the kit will be able to use both .223 and 5.56 NATO ammo Never be spry about asking any question we have all been there learning about guns I learn a lot trying to answer questions here and for that I thank all of you that ask them

If it is chambered in 556 then 223 is no problem at all. But don’t shoot 556 out of a firearm chambered for 223.

Logan, no worries Sir. The Smith and Wesson's M&P Sport 11's barrel is actually stamped 5.56NATO so it will handle both 5.56 and .223 with no issues at all. Cheers!