Really cool. M25operator, have you seen the Beowulf .50 Lower? Just caught it briefly on either the military or discovery channel.
They might have a .50 Beowulf lower stamped special for it, but it uses a standard AR lower. All you have to do is change the top end. Uses a 7.62 bolt. I like the punch the Beowulf packs, kicks like a 20g. Also uses the same mags as .223, they just become single stack. Ammo can be pricey and not easy to find. I believe it was originally designed for the coast guard to stop drug boats.
I don't many options left on the AR platform but I may have to dable in this next.

M25, I'm not familiar with that lower. What is the lever above the trigger?