Essentially, yes. 5.56 is military version of the .223. There's a lot of debate on whether they're interchangeable or not.
http://www.canadiangunnutz.com/foru...s-5-56-x-45-mm-NATO-is-it-safe-to-interchange
They are both rated at 62 366 psi and 55 000 psi.if you look at the pressures they are different the safe overall rule is that if it is stamped 5.56 you can shoot either round if it is stamped .223 you should not... revers is true for .308 and 7.62x51 nato... if it says NATO you should use the lower pressure .308 as the heavy and hot .308 will and I do mean WILL blow your NATO rifle apart in time. I dare you to load 180 Winchester max .308 rounds in an M305 ant if you do I will be stand two counties away.
Alternatively, if you have polished the feed ramp, 50 Beowulf will work..50 BMG or .22



























