Here is an extremely simple modification to enable you to shoot your Barret .50 cal like a P90.
UPDATE: There seems to a problem with certain types of controllers. There are Matrix controllers that use PWM for the LEDs and some which use a different method. To determine the type of yours, remove the battery pack of your controller. Above the right battery terminal, if there is a " TP-19" then it is matrix controller and it will work with this mod. If there isn't a "TP-19" than it is the newer CG version and it will not work.
Step 1: Ingredients
A TT8 Torx Driver
A Small Push Button Switch
Some Thin Wire, Any will do (I used IDE Cable)
An Xbox 360 Controller (Wired or Wireless, it works the same)
A Drill and Drill bit (To match the diameter of the thread on your switch)
Some form of surface to work on. (I used a window ledge, I suggest you don't)
Step 2: Dismantle
There are 7 screws to remove, so grab that Torx driver and twist! (Anti -Clock-wise)
With the buttons facing DOWN , separate the two halves carefully, paying attention to the motors.
Step 3: Drill
Once you have found a place, put the two halves back together and see if there is enough room for your switch to go in.
If there is, well done. Remove the circuit board so that it doesn't get damaged, then you can drill the hole and improve £32 worth of electronics.