Mounts and rings

Rings, bases and adapters for mounting optics on a firearm. This is the component that determines whether an expensive optic delivers on its promise.

Three measurements to check

The tube diameter must match: 25.4 mm (one inch), 30 mm, 34 mm or 35 mm. There are no safe adapters between different sizes.

The height determines eye position relative to the stock. Too low forces the shooter to drop their head, too high to raise it: in either case the position is not repeatable and accuracy suffers. Greater heights are needed by those using a helmet with a night-vision mount or a mask, where dropping the head down to the stock is not practical.

The interface on the firearm: Picatinny and Weaver look similar but are not interchangeable in every case, and pistol red dot footprints — RMR, Docter, ACRO, MOS, RMSc — are all different from one another.

For scopes on AR platforms, cantilever mounts recover the correct eye relief when the rail ends too far to the rear.