Like the description says hunt five big game animals with your handgun. You can get this achievement during the British Columbia hunts. The last hunt in the Idaho Region makes you use the pistol for your first kill with the pistol. The next mission will make you kill two more with a handgun. After that mission you will be hunting a deer from a tree stand. This is a hard and challenging shot, but can be done if you hit the vitals. You will then be required to kill a mountain caribou bull during the next hunt. The achievement will unlock once you claim the trophy.