I have some experiance in hunting crocs.in my part of the world& would like to share it with you.First don't shoot a croc. while it is in water,wait for it to come on land.Crocs.being cold blooded like to bask in the sun especially in the winter season.They have specific timings and you need to know when they will come out of the water.Once the timing is established try to creep up to it as close as possible,making no sound as the slightest noise will make them go back into the water.The best spot for placing the bullet is in the side of the neck where it joins the head the purpose being to get the brain.Anywhere else and its gone.It may die later on but retrieval will be difficult.I have used 270 Win.& 7mm.mag.successfully using solids,try to avoid soft noses.
Hope this helps.