I'm very interested to build a 1000 yard long range hunting rifle.?

If you got the $$$$$ go get a custom rifle made. There is a guy in Pleasanton, Tx at www.riflesinc.com check out what he has on his website cost big bucks though but you are really getting what you pay for. Most people I know that can shoot 1000 yds have 300 ultra mags. I think a .308 could also hold a good group. On YouTube there's a guy that shoots three balloons in a row at 1000 yds.