The zero cost 195 fps Cobra crossbow tuning

The Cobra crossbow is very inexpensive and well made. We have actually used it quite a bit, and even made a 10 shot repeater conversion kit for it. It is powerful enough to kill a Zombie, as ZombieGoBoom demonstrated by testing it against an Ivan Head. But still, it is a bit weak for our taste, The 6,7 gramm bolt travels at about 164 fps, certainly not bad - but can it be enhanced? Yes, and it is simple. Just turning the prod around does the trick. We clocked an average of 195 fps for it, about 42 % more