AR15 converting 9mm to .223

[Lightsped]

I have an Olympic Arms AR15 chambered in 9mm. I would like to buy an .223 upper (complete).

Besides the upper, barrel, charging handle, and bolt carrier is there anything else I would need? Will a .223 upper simply "plug and play" into my 9mm AR15?

 

[AZ Jeff]

IIRC, I think the hammer is different between the 5.56 and 9x19 versions of the AR, and may need to be swapped to get it to run right.

 

[CleverNickname]

The 9mm-style hammer (which is basically an M16 hammer without the hook for the autosear) will work with 9mm and 5.56mm. The 5.56mm style hammer with the notch in the hammer face will only work with 5.56mm.

 

[Lightsped]

The 9mm-style hammer (which is basically an M16 hammer without the hook for the autosear) will work with 9mm and 5.56mm. The 5.56mm style hammer with the notch in the hammer face will only work with 5.56mm.

So if I understand correctly, as far as hammers go, my 9mm hammer will work with .223/5.56? Anything else of concern before I go looking for a .223/5.56 upper?