Canted Base
Also: 20 MOA Base · 30 MOA Base
A scope base machined with built-in downward slope so the elevation turret gains extra usable travel for shooting at long range.
A canted base is a scope base cut with a deliberate forward and downward tilt, commonly expressed as 20 MOA or 30 MOA of built-in cant. By aiming the scope slightly downward relative to the bore, the mount uses up part of the angle a shooter would otherwise have to dial, which frees more of the turret’s range for distance. This is why long range rifles are so often built on a sloped rail rather than a flat one.
The benefit is a higher scope elevation ceiling, since the cant effectively borrows mechanical elevation and hands it back as usable come-up for far targets. The trade is that a heavily canted base can run a scope out of down travel at very short range, so the slope is matched to the intended use. Most of these rails follow the standard Picatinny rail slot pattern, which keeps ring options wide open.