the gunblade does not actually have a barrel. What Kimera noticed was not the barrel, but rather, spindle that the chamber revolves around. If you look VERY carefully, you'll see the start of a barrel at the top of the gun part of the gunblade. However, the blade itself gets in the way of the barrel. Now, the shotgun idea is a bit more sound, since it's possible that a shell is fired from the chamber, hits the blade and turns into slag, which only does a good amount of damage at close range anyway.
