August 21st 2022Tangent Secant, Hybrid — Bullet Geometry Explained By LitzIn ballistics discussions, you’ll find references to “tangent”,…”secant”, and “hybrid”. These terms can be confusing for many readers. Bullet makers sometimes don’t identify their projectiles with secant or tangent designs, adding to the confusion. This article will explain the basic characteristics of tangent, hybrid ogive, and secant bullet designs. The difference between tangent and secant is the hybrid. Most match bullets today have a tangent-ogive profile, while modern VLD-style bullets use a secant profile. Berger Bullets’ latest “Hybrid” projectiles have a blended secant and tangent profile that combines the best characteristics of both nose shapes. The bullet is easier to tune because the secant section reduces drag. The secant section reduces drag, while the tangent section makes it easier to tune the bullet. We reprint Bryan Litz’s glossary section on his Applied Ballistics website. Bryan explains how tangent profiles and secant profiles can be combined to create a hybrid design.
Ogive is often used to refer to the point on a bullet where the curve meets the full bullet diameter. However, the actual ogive is the length of the radius. This radius is often expressed in calibers rather than inches. An 8 ogive 6mm round has an ogive. This is a segment in a circular arc that has a radius 8*.243 = 1.9552. A.30-caliber bullet will have an 8 ogive, but it will have a radius of 2.464″. An ogive that has a radius greater than this will be considered secant. Secant ogives range from very mild (short radius), to very aggressive (long radius). A secant ogive’s radius should be twice as large as the radius of a tangent radius to minimize drag. This means that a tangent oval has an 8-caliber radius. The longest practical secant radius for a nose of the same length is 16 calibers. Ogive Metrics & Rt/R Ratio
LITZ: This number is used to determine how secant an Ogive is. This metric is called the Rt/R ratio. It’s the ratio between the tangent radius and the actual radius of a bullet. In the above example, the Rt/R ratio for the 16 caliber Ogive would be 0.5. The Rt/R value of 0.5 is the lowest practical value and represents the minimum drag for a given length. An ogive with a perfect tangent will have a Rt/R ratio 1.0. Most ogives have an Rt/R between 1.0 and 0.25. The dimensions of the drawings at the end my Applied Ballistics books provide information about the bullets ogive radius and the Rt/R ratio. The Rt/R ratio simply measures how secant an Ogive is. 1.0 is not very secant, while 0.5 is the best of both worlds.
Bryan Litz has created a variety of “Hybrid” design bullets for Berger. Bryan’s design goal was to create a low drag design that is “not finicky” while still achieving the highest possible performance. Normal secant designs (non-hybrid), such as the Berger105gr VLD, have very impressive BC values. However, the bullets can be sensitive about seating depth. Montana’s Tom Mousel set world records using the Berger 105grVLD in his 6mm Dasher. However, he says that “seating depth” is crucial for the best accuracy. Tom claims that a mere.003 is all it takes. A mere.003? seat depth change can make a big difference. Bryan Litz created the hybrid tangent/secant shape to make high-BC bullets more forgiving.
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