I tryed that,

but now I have the fundementals of the script.It doesent work JUST like the halo 2 dual weildeing.

This is how it works

By picking up one weaon, plasmarifle, and by already holding another plasmarifle in your inventory, gives you a profile of the dual plasma rifles.
another script check to see if you ever swith from the dual, and gives you a single and drops a single, hence exiting the dual when picking up or swappin from the dual.
Another third script allows you to hold multiple plasma rifels in the forst place.