For semi automatic and fully automatic gun , they can fire both .223 and 5.56 no problem but if your gun say .223 only on the barrel you shouldn’t fire 5.56 with , it might damage your gun and you , if your gun say 5.56 on the barrel so you can fire both .223 and 5.56 no problem
Little bit different 5.56X45 NATO and .223 REMINGTON, Do you have 5.56 NATO can used .223 If you have .223 Rifle not pretty good for 5.56X45 NATO but you can using.