This was the one thing that made the jetgun even semi-good. The intended way of using it is godawful and most everyone (I would think) probably feels cheated out of a wonder weapon that doesn't take two minutes to kill 24 zombies (the intended way). When I finally figured out about the precharge, I started doing it with claymores, which worked about twice as fast as regular precharge. Now that they've patched that too, I don't see any reason to ever try going for a record breaker on this map again.
Knife precharge just isn't the same and is so much more dangerous (you can't look at the zombies or else you'll lunge at them). The one thing I actually liked about this map...patched, when it was desperately needed.