Make sure to aim high with them!Well yes, I could do that but It'd be a lot more boring than burning cows with a mining laser...
I'll try AFP and see how that goes
Why?
So that they definitely die!
A cow CAN survive a bit of fire, but if you can get them to take a heart or two of fall damage, then they will probably go kaputsky.
However, you need to bear in mind, flinging them through the laser will probably cause the amount of time they are on fire for to decrease drastically :/