[Old Man Dave]

This topic has always fasinated me. I am very much an engineer/maths type geek.

Trouble with using most physics formula are that they are not predictive. There are too many variables. You can apply formula to known data discovered through testing but you can't predict outcomes by imputing known data.

So if someone tests a gun and measures certain perammeters then you could for example calculate the energy generated using a simple formula. I did this in a recent thread. However, calculating the speed (or range) of a gun/spear by equating the energy input (force to load it) doesnt work. You need to know factors related to friction and hydrodynamic resistance. You just can't calculate these values without impirical data.

There are lots of annocdotal stories about speargun performance and most as Mart says are far too general. In its 2008 catalogue Omer gives some figures for performance with different bands which I found interesting but although they were conducted by a firearms testing laboratory they were for "dry" firing. Presumably "out of water", which to me makes them worthless. There are some sites on the net with some tests or data from tests but not nearly enough to make accurate conclusions.

I could write a load more but lets see if this goes anywhere first.

Dave