Chamber to barrel ratio

The chamber to barrel ratio, or C:B ratio, is the volume ratio between the chamber and barrel. The ratio determines how much of the available energy is transferred to the projectile, and a good C:B ratio is a major factor in combustion cannon performance.

Experiments have shown that a C:B ratio of about 0.7:1 is the most efficient for a given chamber. Higher ratio cannons are louder, since more energy is wasted as noise when the projectile exits the barrel.

This does not neccessarily mean that the most efficient ratio is the best to use in a gun, if maximum power is the goal. If the chamber is designed around a certain barrel, a bigger than optimal chamber will give more power since more energy is available. When designing a barrel for a certain chamber though, one near the optimal ratio will make the most of the energy available in the chamber.

In short, C:B ratios are good for determining what barrel is most powerful for a certain chamber, but not what chamber is most powerful for a certain barrel. A near optimal C:B ratio is always good however, if the goal is reduced noise and/or fuel efficiency.

Burst disks can be used to increase the performance of high ratio cannons, since they let higher pressure build up before the projectile starts to move. They will not increase the performance in near optimal cannons. Source

The C:B ratio of pneumatic cannons is much less fixed, since factors like air pressure and valve performance play a greater part in determining overall performance. It is adviceable to use GGDT to determine the best design for pneumatic cannons.