I dont know about as written, but I as a GM wouldn't allow it, seeing how it (IMHO) is a bit of a threat to game balance by creating a "super round". If something like that could be done, why have different types of rounds at all? With a round like what you propose, it would be something that everyone would want to use to the exclusion of all other rounds. Depending on what weapon you are also using it for, the arguement could also be made: why use any other weapon?
Not to discourage, but there are reasons why in every game there are inherant flaws and or defences built in to everything. That way, not one thing will dominate and every single player would want that one thing to the exclusion of everything else.
But that is just me. If your GM will allow it, hey, go for it. The purpose of this game is to have fun. I'm just giving my two cents becasue I have seen in other games things similar to this really mucking things up.