Yes, my friends, what you see in this photograph is the Beowulf bullet, specially designed for an AR-15 automatic rifle [also called the Beowulf rifle]. Here is how one gun enthusiast describes the bullet and rifle:
The Alexander Arms .50 Beowulf cartridge packs awesome power in the AR-15 system. Think of it as a lightweight, handy, semi-auto .45/70 but with a larger diameter bullet and greater velocity. The .50 Beowulf uses a bullet of a true .500 caliber, with loaded ammunition offered from the factory in either a 400-grain soft point or a 325-grain hollow point, with velocities listed at 1800 and 1950 feet-per-second, respectively. This kind of power radically changes the performance aspect of the AR-15 type rifle while retaining the excellent handling and shooting qualities of the weapon. The .50 Beowulf cartridge utilizes possibly the maximum diameter bullet in the biggest case that can be made to reliably function in an AR-15, while operating at a relatively low pressure to assure smooth operation and longevity of the rifle.Oh brave new world, with such weapons and bullets in it! If this sort of thing really intrigues you, you can read more about it here and here. Note also that the same company, Alexander Arms, has also recently developed a Grendel rifle which can shoot targets at even longer range than the Beowulf rifle. Of the Grendel rifle, the company claims, "Currently in testing with the US Military for widespread adoption, the 6.5 Grendel® seems assured a place in history." Oh yeah, baby.