M16 build.

[MT2008]

Originally Posted by Yournamehere

I know that, but 5.56 is loaded to higher pressures, and is what the military uses in their guns. I'm saying if the lower half of the gun is for the lower pressure round (.223), is the gun safe to shoot without KBs?

With the exception of the buffer tube, I can't think of any components in the lower receiver that would even be affected by higher pressure.

Anyway, I am not aware of any AR-15 lowers that are built specially for military-grade ammo and others built to handle civilian ammo (which isn't to say there's no difference between an M16 and an AR-15 lower, but those differences have to do with ability to fire on automatic, not ammo types).