i know you can get the system volume out of 100 with
get output volume of (get volume settings)
and set it out of 7 with
volume 7
this seems a little strange, is there way to set the system volume out of 100 also?
Their is actually a script in the scripts folder of OS X that shows you how to do this.
Instead of just using whole numbers like 7, use decimals such as .50 for half volume. I hope you were paying attention in Math Class 
The 0…7 scale is old and deprecated. It exists only for legacy support.
Instead you should use the newer format of the command:
set volume output volume 50
The ‘set volume output volume’ command uses the same 0…100 scale as 'output volume of (get volume settings)