I found out how to fire 10 Marshall shots in 3 secs with out this perk ... ehm i forgot the name... with that you can fire faster.
So how to do this :
1. Take a Marshall
2. Throw away your grand or the Grandlouncher (just fire).
3. Shot with the Marshall
4. Double Tap your Weapon Switch buttom ( I think default it is "2" )
5. Shot again with your Marshall.
6. Repeat 3 and 4 many times.
Explanation :
If you double Tap the Weapon Switch buttom you cancel the "Pump Action" ehm the "Reload" ... i dont now the right word to decribe it ...
Pro Tipp:
If you have a good Gaming Mouse like the Rat7 you can write a short Macro so you dont need to double Tap your Weapon Switch buttom, just press the new macro ones.
PS.: Sorry for my bad English