Ideal C:B ratio?

[Joemama55]

Ive been attempting to build a perfect combustion spudgun which uses a propellant such as butane, but im struggling to find the best C:B ratio as one half of the internet says to use 0.8:1 and the other 1.5:5. My current build (not glued togther yet) is 1.5:1 but i wanted to know whether i should change this or keep it.

[mark.f]

The 0.8:1 ratio comes from burntlatke's testing where chamber volume was held constant and barrel volume was changed, which effectively found the longest barrel length that could efficiently use a certain chamber size.
Increasing chamber size up to a certain point will just lose efficiency. You could try using HGDT to model your cannon instead.

[D_Hall]

The 0.8:1 ratio comes from burntlatke's testing where chamber volume was held constant and barrel volume was changed, which effectively found the longest barrel length that could efficiently use a certain chamber size..

It is worth noting, however, that latke was using potatoes for projectiles and PVC as his building material. Nothing wrong with that, mind you. But changing projectile mass and material will have an effect on efficiency due to residency effects. Changing the barrel material will absorb more/less heat energy and friction coefficients. Thus, the "ideal" ratio is going to change depending on exactly what you're doing, OP. This is not to say that latke was wrong. It is to point out that there is no universal answer. The real answer is "It depends....".

[jackssmirkingrevenge]

You could try using HGDT to model your cannon instead.

Seconded, and as the creator of said program has expounded above, the real answer is "it depends" and HGDT goes a long way in giving a very good idea of how those variables will affect performance and efficiency.