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When properly made express sights are first installed, ELEVATION WILL BE HIGH - it's SUPPOSED to be. The height of the rear V is made high on purpose, so that correct elevation can be properly filed in. When new express sights are properly installed on a double rifle by a gunsmith that knows what he's doing, he first fires it with the load it was regulated with. Elevation will be high. He then files the rear V, shoots again, files some more, etc., until elevation is properly filed in with the sight picture specified by the customer.

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This is a problem of similar triangles. The sight radius (r) and range (R) are congruent legs, and the front sight height change (h) and impact change (H) are congruent legs. All measurements must be in the same units. Therefore:

h/r = H/R or equivalently h = (Hr)/R

Example: sight radius 20 inches, range 1800 inches (50 yards), impact change 8 inches.
h = 8(20)/1800 = 0.089 inches.

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