August 4, 2021
You’ll often hear references to “tangent”,’secant” and “hybrid”, when discussing ballistics. 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 provide a basic explanation about tangent, secant and hybrid ogive bullet designs to help you understand the characteristics these three basic shapes.
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’s secant section reduces drag while the bullet’s tangent section makes it easier to tune. Bullet seating depth position is less sensitive.
Bryan Litz, Berger Bullets’ ballistician, explains tangent bullet ogive designs in a glossary section on his Applied Ballistics website. We reprint it below. Bryan explains how tangent profiles and secant profiles can be combined to create a hybrid design.
How bullet Ogive curves are defined
Although “ogive” is commonly used to describe the point on the bullet where the curve meets the full bullet diameter, the actual meaning of “ogive,” is that the entire bullet curve from the tip to its straight section (the shank)
How is the ogive described?
LITZ: The length of the bullet’s radius is what defines its ogive. This radius is often expressed in calibers rather than inches. An 8 ogive 6mm round bullet has an ogive. This is a segment of an arc with a radius 8*.243 = 1.9552. An 8 ogive bullet in.30 caliber will have the same radius as an 8 ogive bullet in 6mm, but it will have a radius of 2.464 inches for a.30 caliber bullet.
If an ogive is perfectly parallel to a given length of nose, it will have a specific radius. An ogive will be secant if it has a radius greater than that. 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 if a tangent oval has an 8 caliber radius, then its practical secant radius is 16 calibers for a given nose length.
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 most secant.
Hybrid Bullet Design – 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.
Similar Posts
Tags: Applied Ballistics. Bryan Litz. High BC Bullets. Hybrid Bullet. Hybrid Ogive. Seating Depth. Secant. Tangent Ogive.
