Ok, Paul's is more efficient than it is blocky. I want to like AKA guns, but I can't. I should- intellectually I dig 'em, but I just don't feel any chemistry. How can you make a solid gun, with low operating pressure and a very light bolt, and have it kick so much? Mind you, it slowly bucks upward in a steady direction, but the force as you shoot a steady rope of paint is surprising. This is my biggest beef with Vikings.
To the original question- there must be a damaged seal or something. I am not really conversant in the specifics of Bushmaster 2000s, but 400 shots is terrible on any tank.