American Rifle Company developed an advanced scope mounting system for the Mausingfield that provides the security of an integrally machined rail and the interchangeability of a removable rail.
When a typical rifle is fired, it undergoes high rates of acceleration, on the order of 200 to 300 g’s, thereby imparting high forces to the scope mounting system. These forces can cause slippage between the receiver and the mounting system, ultimately resulting in sight misalignment and reduced accuracy. This is especially true if only friction is relied upon to maintain the relationship between the scope mounting system and the receiver, as is predominantly the case with the Remington M700 and many of its clones.
A receiver having an integrally machined rail eliminates the possibility of slippage. However, in order to better utilize the available range of elevation adjustment within a scope, a rail must be inclined with respect to the rifle’s bore. But different scopes require different amounts of inclination, making integrally machined rails a bit encumbering when you are selecting a scope.
Ideally, the connection between the rifle and the scope should be rock solid, while also affording the shooter the ability to replace one scope for another which may be better suited for a different application. To fulfill these requirements, the Mausingfield receiver has an integral key with tapered walls that engages a similarly tapered slot within the rail. Five commercially available 8-36 x ¼” long socket head cap screws are used to draw the receiver and the rail together. The resulting interlocking connection makes slippage between the two impossible, thus providing both security and interchangeability.
To choose the rail angle that will make available most of the elevation adjustment within the scope, you need to determine how much elevation adjustment the scope has, divide that number by two, and then subtract either 15 MOA or 4.4 milliradians. 15 MOA (or 4.4 mils) is subtracted because approximately 6 MOA (1.7 mils) must be allocated to obtaining a 100 yard (or 100 m) zero, assuming the scope is mounted approximately 2” (50mm) above the bore. In addition, approximately 9 MOA (2.6 mils) must be allocated for build tolerances of the rifle, the scope mount, and the scope. This is an approximation, but it is more than adequate for choosing the rail angle. In general, 20 MOA (5.8 mils) is appropriate for scopes having 30mm tube diameters, and 30 MOA (8.7 mils) is appropriate for scopes having 34mm tubes.