Okay so i recorded me and my friend with a timer to show how fast each round would take when farming. you can earn two achievements this way. one of course is Mad Skillz with farming Skill Points and the other is "B.O.W.s are Ugly" by of course killing the BOWs.
Chris and Piers Campaign
should be completed.
Load up Chris and Piers Campaign, Chapter 5. Doesnt matter the difficulty, and solo or co-op doesn't matter. In the video below I used a partner to shut off the fans before i got there and help kill the BOW's to speed up the process.
Just skim thru the beginning part of the level by dodging regular enemies and skipping cut scenes as fast as possible, until you get to the 2nd elevator which to a circular room with levers all around the room.
After activating the "Co-op Levers" to progress there will be a timer and which at the same time enemies will start release BOW's by pulling levers around the circular room. There are a total of 5 Levers that release 2 BOW's at once, and only 2 Levers can be pulled until all BOW's are destroyed. So in other words are a total of 10 BOW's that need taking care of before progressing.
(*NOTE* Don't Forget the Skill Points the B.O.W.'s Drop. That's Your 20K)
After Defeating all B.O.W.'s and the timer is done, go ahead to the next room in which there will be a cut scene that involve Chris and Piers meeting up with Jake and Sherry. Skip the cutscene and watch your top left corner of your screen. It should say saving. After saving go and end your game, then rinse and repeat the process