That's the AA12 firing Frag12 rounds, that I mentioned earlier. Edit: This weapon - http://en.wikipedia.org/wiki/Atchisson_Assault_Shotgun View: http://www.youtube.com/watch?v=NdEyP5P0rYs I know people who have described the AA12 with Frag12's as being the closest thing to a Boltgun the modern world has. You do know that you're comparing the Round's size to the Boltgun's Muzzle Brake/Recoil Compensator (designed to use the rounds propellant gases to counter recoil and rise) and not the actual barrel? http://en.wikipedia.org/wiki/Muzzle_brake I pointed that out when Laanshor posted the above a month or more ago. Also, comparing a 40K Bolt Round to modern one doesn't work. Modern rounds are made from steel, brass, and lead with a nitrocellulose and nitroglycerine (Cordite) mix for propellant. The Bolt Round can be made from Plasteel, even Adamantium, with a Diamantine (artificial Diamond) tip, and uses Fyceline for Propellant. It's a round that was refined over Millennia during Earth's first interstellar empire.