This is the mighty AR500 Auto Max from Big Horn Armory. https://www.bighornarmory.com/ This is one sexy beast and way more pleasant to shoot that you would expect from such a large bore rifle. In this video I go over the features of the weapon as well as discus the ammo that's available at this time.
At this time three ammo manufactures make ammo, Underwood, https://www.underwoodammo.com/ Buffalo bore, https://www.buffalobore.com/ and Steinel ammo, https://www.steinelammo.com/ I highly recommend all three for great high quality ammo, not just for the 500 Auto Max.
And finally, I would like to thank TL Tactical for the use of their lanes, be sure to visit them as well, https://tltacticalfirearms.com/index.html