Here's the deal. In the early days of spudgunning, there wasn't a great deal of precision involved. Poorly made guns had a nasty tendancy of exploding in people's hands. As always, there was the tradeoff between power and safety. To avoid back yard disasters, a safety factor was adopted by most people. If the volume of a gun's combustion chamber was not more than 1.5 times bigger than that of the barrel, the gun would be pretty powerful, but more importantly, the odds of the gun blowing up were pretty low. Performance was not the driving force behind the adoption of the 1.5:1 ratio. Safety was.
For the most part, the ratio is still the best way to go for a beginner. It gives plenty of power, and ensures a fair amount of safety. However, independant tests have shown that optimum performance is acheived with much lower ratios, but there is still much confusion.
The same kind of ratio stigma exists with pneumatic guns. It's widely believed that c:b ratios of 3 or 4 to 1 are optimum for any and all pneumatic gun. Pneumatics avoid the safety concerns of explosive propellants, but large air chambers can get very bulky very quicky. The tradeoff in this case is between power and convenience. A gun with a 4:1 ratio is quite powerfull, but not terribly bulky.
As I will explain, many people have misconstrued these numbers as requirements for optimum performance. This is mainly due to the fact that people naturally begin designing a gun by starting with the barrel, which makes the concept of optimization difficult to grasp. Next, I'll begin to lay down the basic principles for truly maximizing the power of a spudgun.