M16 build.

[Gunmaster45]

5.56x45mm is military metric. .223 Remington is in caliber inches. They are the same bullet all in all.

[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?

[Gunmaster45]

I'd say it would work fine then, the difference isn't that drastic.

[Nyles]

As I said earlier, no difference. It's safe to interchange the ammo anyways, and the lower is not a pressure-bearing part. Even if the upper is in a completley different calibre, the lower makes no difference as long as the mag fits - 6.8mm SPC upper, for example, fits fine on a .223 lower.

[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).