I am Texas Country Boy
I am looking to buy a Sig Holo 556 and I need to know if a .223 will safely fire in the 556?
some will and some wont just depends on the weapon
you should be able to fire a .223 out of a 5.56 without any problem, just don't fire a 5.56 out of a rifle that is made to only shoot .223. the 5.56 is loaded to higher pressure.
5.56 has a deeper chamber than the .223 round