Scope ring height and objective clearance

Ring height is the distance from the top of the rail to the centre of the scope tube. On a Picatinny rail the common categories are low at about.850 in, medium at about.990 in and high at about 1.275 in.

The objective bell has to clear both the barrel and any rail or forend under it. A larger objective sits lower for a given ring, so as the objective grows you step up the ring height. Low rings suit small objectives up to about 44 mm, medium rings are the safe choice for a 50 mm objective on a 30 mm tube.

Two makers measure differently. Vortex, Athlon and Seekins quote the centre height, the rail top to the tube centreline. Talley and Burris quote to the bottom of the ring cradle, so to compare add the tube radius, half an inch for a 1 inch tube. A.400 in Talley low ring is not a.400 in centre-height ring.

Fit the lowest rings that still clear the objective, and measure the outer diameter of the bell rather than the advertised glass size, since a 50 mm scope often has an outer bell nearer 56 mm.