If you will be shooting from a standing position, the length of the barrel will affect the balance of the gun and therefore your ability to hold a steady aim. If shooting from a prone or Creedmore position (on your back), balance is much less of a factor. For 100 yards, I shoot a .357 Magnum Ruger revolver with a 4x scope, a .22 caliber Ruger Mark II (at small rimfire targets), and a .45 Colt Ruger Bisley with a 2X scope. For the 200 yard course, I don't think you'd want less than a .44 Magnum. Especially since the 200 yard targets are quite heavy and difficult to knock over. I use a Remington XP100 in 7mm Benchrest caliber for the 200 yard course. It carries a variable power scope set to 5X.