You will benefit from learning iguana characteristics. They are social, have habits, cautious about new surroundings. Google info search fair. If you read pet owner comments you will learn a lot more. Shot placement is very important. The are also great swimmers and can stay submerged for long time. I have seen wounded ones bagged and placed in a freezer for humane finish. Some neighborhood associations contract for removal. .22 cal will work fine for a good shooter. Extra shots likely needed at times and that limits break barrel choices. Gamo Swarm 10 shot ?