I had the pleasure of closing the hole caused by a piece of case brass in the forehead of an unexperienced reloader about a year ago. Besides stuffing the bullets (.357 magnum) to the rim with powder, his loader also used powder that hat become wet and had deteriorated to a very fine pulverized powder. The pressure was large enough to crack the cylinder in half, blow the bridge off the revolver and logde part of the brass case in the shooters forehead.
I removed the remaining rounds from the other cylinder half, pulled the bullets and examined the powder. Of the 2 rounds, one was ok, the other was also an accident waiting to happen. The cause was mainly a shipment of powder gone bad, but also lack of care and knowledge during reloading.
So the 'breathing space' in a case is definitely there for a reason