The scope base mounting system that utilizes the flat rail with crosswise slots found on most firearms is the Weaver style. This base is 7/8-inch wide and accepts Weaver style rings. Crosswise, protruding rails beneath the rings help prevent movement due to recoil. The Weaver rings are easily detached from the base without removing the scope. They can then be reattached. This type of base allows for easy swapping of scopes from one gun to another.
The Picatinny scope base is a one- or two- piece design made of steel. Badger Ordnance manufactures a two-piece base using the Picatinny system, available in a couple of different MOA's (minutes of angle). It secures scope rings in place with more flexibility than some other ring-and-base systems. The Picatinny is used on both tactical and sporting rifles. This scope base is easily installed since it uses factory-drilled scope base holes and screws. It will accommodate both right- and left-hand receivers. This scope base can be adjusted to several different lengths of scope bodies. Weaver rings will fit Picatinny bases, but Picatinny rings are not compatible with Weaver bases. This is the most versatile of scope bases. In the 1960s, the Picatinny Arsenal in New York set about creating a stronger scope base for heavy weapons. The result was a base that has several uses in law enforcement and the military. The base can be also used to hold flashlights, night vision devices and laser sights firmly in place.
One of the oldest scope mounting systems is known as dovetail. The rotary dovetail is one of the oldest methods for holding a scope. This scope base system is heavy and strong. These bases and rings are called Redfield style, as they were patented by John Redfield. The dual dovetail is sturdy and is used by hunters with rifles that have strong recoil. As an example, the dovetail has been used successfully on both the .300 Winchester Magnum and the .338 Winchester Magnum. These two rifles are extremely heavy, but the Redfield dovetail stood up to the recoil with no loss in accuracy.