Reloading Glossary of Terms
There are 3 names in this directory beginning with the letter S.
Sectional density (SD)
When referring to a bullet, the Sectional density (SD) refers to the weight of the projectile relative to its caliber. SD is most often used when comparing the penetrating ability of a projectile in one caliber to another.
Second Focal Plane. Referring to a rifle scope which has the reticle on the second focal plane so the reticle is not changed when increasing or decreasing magnification as it does not move.
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