Back in the early 80s, 400 yards was long range to me and anything over 500 yards was extreme long range (the ballistic charts in the Remington catalog and my reloading manual didn’t go over 500 yards). At that time, I heard of a group of guys in northern Idaho who were using 50 BMGs and big military rangefinders for elk clear out to 1000 yards or more. Not too much later, the regulations in Idaho changed to prohibit the use of a rifle that weighed more than 16 pounds with scope, sling, and other attachments. Although I am sure someone could build a 16 pound 50, I don’t think I would want to shoot it.
It is amazing how equipment and effective hunting ranges have changed since then.