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Eh, now, I know the boogers jump around a lot, but I'd imagine it's no harder than killing a lagging flea in mw4.
Don't chase the toads with your reticule. Chasing any target with a reticule is the best way to miss. Figure out when they will be the most exposed (apex of jump has already been mentioned), put the reticule there, watch them, and time the shot. This will reduce any corrections you must make to a minimum.
If you've got the room, you might also try flipping the throttle into full reverse, and thus exposing them to your front firing arc for more time.
I can't say enough though... dont chase with the reticule. Time the shot. Spend your time and brainpower trying to figure out where they will be the most exposed for the longest time. It will give you better results.
Doing so will get you better results with *any* direct fire weapon.