I own a double for the purpose of getting very close to elephants. So the caliber should be the biggest that I can handle. However, I am not brute enough to carry a 13 to 16 pound rifle on a long stalk. So that leaves out the .577 and .600. Thus I settled on the .500 NE as being the most power I could get out of a double in a rifle light enough for me to carry on a long stalk at a rapid pace.