Thoughts? This would definitely add a couple pounds of weight to your AR. I'd prefer to just carry a sidearm on my my side, not in the stock of my gun. I like the way they were thinking however... I would prefer to slide a loaded PMAG in the butt of my stock as an emergency mag of ammo if needed.
http://www.guns.com/2015/01/22/mule-tactical-unveils-ar15-hidden-glock-stock/