Starline Brass recently added.300 Blackout to their growing line-up of quality rifle brass, which will soon include .450 Bushmaster, .243 Win., .223 Rem., 6.5 Creedmoor (small and large primer pockets), 7mm-08 and .260 Rem. The new .300 Blackout rifle brass is available at half the price of comparable cases.
Some history: the .300 Blackout was introduced in 2009 by Advanced Armament Corporation for the AR15 platform. Any standard 5.56mm AR15 can easily be converted to .300 Blackout by changing the barrel. Its intention is to be loaded at subsonic velocities and fired in a suppressed rifle. The popularity of the .300 Blackout cartridge has led to it being offered in many bolt-action and single-shot rifles, which allows it to be loaded at subsonic velocities with any bullet weight, without concerns about cycling.
The .300 Blackout is the first SAAMI standardized round based on the .300/.221 Fireball wildcats, though the Blackout was designed to be built off of the 5.56mm case.