[Lightsped]

I have an Olympic Arms 9mm AR. What do I need to buy to convert it to a .223? Upper receiver, bolt carrier, charging handle, and anything else?

 

[Ducman]

If it has a standard magwell that will fit a standard mag then you should be OK with a complete upper...barrel,bolt, etc

but there may be problems with the hammer. I recall them being different on 9mm complete guns, but I could be wrong

 

[fatcat]

Some hammer springs are lighter impact and need to be changed to the full 223, This is mainly because the 5.56mm military primers on some ammo are harder than others so some have strong springs in them. Try it without or just go and change it, its only a few bucks.

 

[Adler]

Or just throw some Euro ammo through it and see how it fires. Some Geco ot Dynamit Nobel, if not Fiocchi. Euro primers are harder as well and thats the main reason that they went to inertia firing pins later than we did.