Traditionally, rifles were built with fixed front and rear iron sights, or with a rear iron sight ladder for aiming at long distance targets. Today, the optical scope is the preferred choice of many hunters and shooting enthusiasts because it magnifies the target image. In order to have a scope, you need to have it mounted. This depends on the design of the rifle and its base or rail, on which the scope mount is secured. Once you've determined what kind of base or rail you have, choosing the appropriate mount will be easy.
Look on top of the rifle receiver. Most rifles manufactured today have either a Standard rail, or a Weaver rail. Weaver rails are sometimes referred to as Picatinny or Tactical. A Standard rail has two grooved lines running along the full length of the rifle receiver. The grooves will be spaced between 9 and 13mm apart. A Weaver rail is slightly wider, and will have these same grooves but spaced 20 to 22mm apart. Some Weaver rails have horizontal braces across the grooves, or are equipped with arrester blocks.
Identify the rifle attributes. Rifles are typically bolt action or lever action, while some high powered rifles are semi automatic with a bolt or rear charging handle. If you use a bolt action or a top magazine rifle, you need a scope mount that won't interfere with the bolt movement or magazine. Single piece mounts are ideal for lever action, bottom magazine, or rear charging handle rifles. Two-piece mounts are required for bolt action or top magazine rifles, because they are spaced out to allow access and movement for the bolt or magazine.
Decide the average distance that you'll be shooting for most of the time. Tapered mounts are ideal for those who intend to shoot at 500 yards or greater. If you don't plan to shoot at this distance or beyond, choose a flat mount.
Determine the scope size that you'll be using, then combine the knowledge of your rail and rifle attributes, and select your mount. If you have a standard base used on most low-powered rifles, or air rifles, and you want to install a scope with a 25mm tube, any high or medium standard mount will fit perfectly. If you own a high-powered rifle with a 20mm base rail, and your scope has a 30mm tube, you'll be best suited with a high 30mm Weaver mount.
Ask a local gunsmith about scope mounts to get a knowledgeable recommendation on mounts for your scope.
Never point a weapon at anything that you do not intend to shoot or kill.