Sited in at 25 yards will get you on paper at 100 yards with most conventional hunting rifles and sight combinations.
As GC stated, the described method is referred to as Battlesight Zero with the standard 20" M-16 rifle sights. During the 1970's at the start of the first Arab/Israeli War, some of the plane loads of M-16 rifles hastily sent to the the Israelis had the sights initially calibrated in this manner during the flights by Army technicians. Once in Israeli hands, they were immediately put into combat use and were found to be "combat accurate" at extended ranges in the desert versus the Saudis and the Syrians.
Anyone who hunts at extended distances beyond 100 yards needs to shoot the rifle used to know where its actually hitting at those ranges. A rifle sited to impact roughly 1.5" above point of aim on a target at 100 yards will usually allow you to hit an animal at normal reasonable hunting/extended ranges unless you're into extreme long range hunting. Then twisting nobs, etc. and actually shooting at those extreme extended ranges again is the ony way to really know.
No matter what range is being hunted at, shooting the rifle is the only real way to know where you will be hitting.
