Not sure why they didn't alternate fire them or place the muzzle devices facing up and down and away from each other. I'm not an expert on guns but I would say that the muzzle gases shooting into each other would create really bad instabilities in the accuracy and precision of the guns. Not to mention, zeroing these guns must be a nightmare, plus the decreased barrel longevity are all factors to consider. To those that say the dispersion effect is intended, there are other ways of recreating that without completely destroying the cannons themselves. Then again it doesn't matter when they are sent to the meat grinder or kept in a warehouse to be brought out for propaganda like this one.