A tangential ogive is tangent to the front band (or tangential to the bore riding section, on a bore riding nose.
My secant ogive doubles that radius. In theory, a secant ogive could be any radius greater than a tangential ogive, but I chose 2X because it is simple to program.
Secants are used on jacketed bullets because they improve the ballistic coefficient very slightly. Hornady spire points are an example of a secant ogive.
CB shooters usually don't care about ballistic coefficient. We do care about chambering and how far the bullet has to jump until it contacts the rifling (or the revolver throat). The secant makes the crimp-to-throat distance a little shorter and a little easier to predict. For that reason, a secant is sometimes used in short-throated firearms like Freedom Arms revolvers and some leverguns.
Original LBT designs made by Veral were more or less tangential. However, "imitation" LBT bullets are sometimes secants, probably because the secant is more likely to chamber in tight-throated guns..