On Monday, March 7, 2016 at 5:34:50 PM UTC-5, wrote:
On Mon, 7 Mar 2016 13:52:21 -0600, "Ryan P."
wrote:

I'm happy with my AR-10. Its a little heavier than AR-15's I've shot,
but I like the extra oompf of a .308.

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I believe you can put a .308 upper on an AR-15 lower. Please correct
me if I'm wrong.

The .308 magazine won't fit into a standard AR15 magazine well. There are custom ones. For the standard lower, the .300 Blackout or 7.62x39 is the way to go.