one of the reasons i love my state of SC and the county i live in we can do almost anything we want on private land. "the way it should be" we can hunt with any black powder caliber and any centerfire. we have freedom! i have been hunting all my life i am 63 and have never had a game warden come on any private land and ask me anything. that being said we have a personal and ethical responsibility to game animals. personally i think if you are a seasoned hunter with self control a 40 is fine for deer up to 150 lbs. or so. if you don't feel comfortable with a smaller caliber get a bigger one. it is all about shot placement and penetration no matter what caliber you use,,,,,,,,,,