just repetitive muscle memory. If you stick with one rifle and learn it well you will become master of your domain.
Shot out to 100yds for the first time in my life this evening at Atterbury. Stockish M&P15 Sport. Vortex Viper 6.5-20x50. Store bought 69gr Winchester Match. Shooting off the bench with a bipod. Average group was 1.42". Best was .75". Not great but not horrible I guess.