This article, which originally appeared in the Sierra Bullets Blog, provides a new terminology that helps describe the geometry of bullets. Once you understand the meaning of “Caliber(s) of Ogive”, you can quickly evaluate potential bullet performance by comparing listed Caliber of Ogive numeric values.
by Mark Walker, Sierra Bullets New Product Development Manager
During one of our recent product releases, we listed the “caliber of ogive” of the bullet in the product description. While some understood what that number meant, it appears that some are not aware of what the number is and why it is important. In a nutshell, the “caliber of ogive” number will tell you how sleek the front end of the bullet is. The higher the number is, the sleeker the bullet. It also makes it easy to compare the ogives of different caliber bullets. If you want to know if a certain .308 caliber bullet is sleeker than a 7mm bullet, simply compare their “caliber of ogive” numbers.
So exactly how do you figure “caliber of ogive”? If you look at the drawing of the .30 caliber 175 gr HPBT bullet #2275 (at top), you will see that the actual radius of the ogive is 2.240. If you take that 2.240 ogive radius and divide by the diameter (or caliber) of the bullet you would get 7.27 “calibers of ogive” (2.240 ÷ .308 = 7.27). (See top photo).
In a nutshell, the “caliber of ogive” number will tell you how sleek the front end of the bullet is. The higher the number is, the sleeker the bullet.
Next let’s look at the print (below) of our 6.5mm 142gr HPBT #1742 bullet for comparison. The actual radius of the ogive is 2.756. Like with the .30 caliber 175 gr HPBT bullet #2275, if you divide 2.756 by the diameter (or caliber) of the bullet you get 10.44 “calibers of ogive”.
Some people would say why not just compare the actual ogive radius dimensions instead of using the “caliber of ogive” figure. If we were comparing only bullets of the exact same diameter, then that would be a reasonable thought process. However, that idea falls apart when you start trying to compare the ogives of bullets of different diameters. As you can see with the two bullets presented above, if we compare the actual ogive radius dimensions of both bullets the difference is not much at all.
However, once again, testing has shown that the 6.5mm 142 gr HPBT #1742 has a significantly higher BC. The only way that this significant increase shows up, other than when we fire the bullets in testing, is by comparing the “caliber of ogive” measurement from both bullets.
Hopefully this will help explain what we mean when we talk about “caliber of ogive” and why it’s a handy number to use when comparing bullets. This information will help you to make an informed decision the next time you are in the market to buy bullets.
Story tip from Grant Ubl. We welcome reader submissions.
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SHOT Show 2016 kicks off in two weeks in Las Vegas. While at SHOT Show next month, we plan to get the “inside scoop” on new bullet designs from Berger, Hornady, Lapua, Nosler and Sierra.
A while back, at SHOT Show 2012 we chatted with Berger Ballistician Bryan Litz about Berger’s popular line of Hybrid bullets. Berger now offers a wide range of Hybrids in multiple calibers and weights. In fact, for .30-Caliber shooters, Berger now offers seven different Hybrid match bullets, with weights from 155 grains up to 230 grains. Two .338-caliber OTM Tactical Hybrids were introduced in 2012 (a 250-grainer and a 300-grainer).
Bryan tells us: “The hybrid design is Berger’s solution to the age old problem of precision vs. ease of use. This design is making life easier for handloaders as well as providing opportunities for commercial ammo loaders who need to offer a high performance round that also shoots precisely in many rifles with various chamber/throat configurations.”
For those not familiar with Hybrid bullets, the Hybrid design blends two common bullet nose shapes on the front section of the bullet (from the tip to the start of the bearing surface). Most of the curved section of the bullet has a Secant (VLD-style) ogive for low drag. This then blends in a Tangent-style ogive curve further back, where the bullet first contacts the rifling. The Tangent section makes seating depth less critical to accuracy, so the Hybrid bullet can shoot well through a range of seating depths, even though it has a very high Ballistic Coefficient (BC).
In the video we asked Bryan for recommended seating depths for 7mm and .30-Caliber Hybrid bullets. Bryan advises that, as a starting point, Hybrid bullets be seated .015″ (fifteen thousandths) off the lands in most barrels. Watch the video for more tips how to optimize your loads with Hybrid bullets.
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In the Berger Bulletin this week is a further discussion of the new Berger “Hybrid” bullet design. This combines a secant ogive shape in the front of the bullet with a tangent ogive shape near the full-diameter (shank) section. Currently the Berger Hybrid is available in .338 caliber and 7mm. Berger will soon release a new hybrid .30 caliber bullet, with 6mm and 6.5mm hybrid projectiles to follow.
How the Hybrid was Developed
In the late 80s, the VLD was born. This design allowed shooters to use lighter bullets and smaller calibers to achieve the same or better trajectory than heavier bullets in bigger calibers. Lighter bullets shot in small calibers were easier on shooters resulting in higher scores and an improved shooting experience. But, this improvement came with a price. Each shooter had to adjust their load in each rifle until they could get the VLD bullet to shoot precisely. Once the load was dialed in, the VLD was one of the most efficient bullet designs in history. But this didn’t stop shooters from yearning for a bullet that is easier to tune.
The VLD design was created by Bill Davis who was one of the top ballistic minds during this time. His [designs] have made a tremendous impact on how long range shooting over the last two decades. One might think that nothing this good can be improved upon. But it could… Ballistician Bryan Litz recognized both the advantages and disadvantages of the VLD design. He went to work to see if he could keep the good results the VLD produced while reducing its sensitivity to seating depth. His efforts have produced the Berger Hybrid.
The Berger Hybrid design incorporates two different shapes within the nose. As the bearing surface ends, a tangent ogive begins. This tangent section of the ogive results in the bullet being much less sensitive to seating depth. Testing results show that the Berger Hybrid shoot equally well at either a jam or a jump. As you move forward along the tangent portion, the shape changes into a secant ogive. The secant ogive is the shape used on the VLD bullets. This shape is very efficient in the wind and is why the VLD became so popular.
By bringing these two shapes together, Bryan has successfully created a bullet that is both not sensitive to seating depth and shoots very flat like a VLD. The key to all this is not just the combining of these two shapes, but also the partnership between the ballistician and the bullet maker.
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In discussions of ballistics, you’ll see references to “tangent” and “secant” bullet shapes. We know that, for many readers, these terms can be confusing. To add to the confusion, bullet makers don’t always identify their projectiles as secant or tangent designs. This article provides a basic explanation of tangent and secant designs, to help you understand the characteristics of both bullet shapes.
Tangent Ogive vs. Secant Ogive vs. Hybrid
Most match bullets produced today use a tangent ogive profile, but the modern VLD-style bullets employ a secant profile. To further complicate matters, the latest generation of “Hybrid” projectiles from Berger Bullets feature a blended secant + tangent profile to combine the best qualities of both nose shapes. The secant section provides reduced drag, while the tangent section makes the bullet easier to tune, i.e. less sensitive to seating depth position.
Berger Bullets ballistician Bryan Litz explains tangent and secant bullet ogive designs in a glossary section of his Applied Ballistics website, which we reprint below. Bryan then explains how tangent and secant profiles can be combined in a “hybrid” design.
How Bullet Ogive Curves are Defined
While the term “ogive” is often used to describe the particular point on the bullet where the curve reaches full bullet diameter, in fact the “ogive” properly refers to the entire curve of the bullet from the tip to the full-diameter straight section — the shank. Understanding then, that the ogive is a curve, how is that curve described?
LITZ: The ogive of a bullet is usually characterized by the length of its radius. This radius is often given in calibers instead of inches. For example, an 8 ogive 6mm bullet has an ogive that is a segment of a circular arc with a radius of 8*.243 = 1.952”. A .30-caliber bullet with an 8 ogive will be proportionally the same as the 8 ogive 6mm bullet, but the actual radius will be 2.464” for the .30 caliber bullet.
For a given nose length, if an ogive is perfectly tangent, it will have a very specific radius. Any radius longer than that will cause the ogive to be secant. Secant ogives can range from very mild (short radius) to very aggressive (long radius). The drag of a secant ogive is minimized when its radius is twice as long as a tangent ogive radius. In other words, if a tangent ogive has an 8 caliber radius, then the longest practical secant ogive radius is 16 calibers long for a given nose length.”
Secant Ogive vs. Tangent Ogive
Ogive metrics, and Rt/R
LITZ: There is a number that’s used to quantify how secant an ogive is. The metric is known as the Rt/R ratio and it’s the ratio of the tangent ogive radius to the actual ogive radius for a given bullet. In the above example, the 16 caliber ogive would have an Rt/R ratio of 0.5. The number 0.5 is therefore the lowest practical value for the Rt/R ratio, and represents the minimum drag ogive for a given length. An ogive that’s perfectly tangent will have an Rt/R ratio of 1.0. Most ogives are in between an Rt/R of 1.0 and 0.5. The dimensioned drawings at the end of my Applied Ballistics book provide the bullets ogive radius in calibers, as well as the Rt/R ratio. In short, the Rt/R ratio is simply a measure of how secant an ogive is. 1.0 is not secant at all, 0.5 is as secant as it gets.
Hybrid Bullet Design — Best of Both Worlds?
Bryan Litz has been developing a number of modern “Hybrid” design bullets for Berger. The objective of Bryan’s design work has been to achieve a very low drag design that is also “not finicky”. Normal (non-hybrid) secant designs, such as the Berger 105gr VLD, deliver very impressive BC values, but the bullets can be sensitive to seating depth. Montana’s Tom Mousel has set world records with the Berger 105gr VLD in his 6mm Dasher, but he tells us “seating depth is critical to the best accuracy”. Tom says a change of .005″ in seating depth “can cause the group size to increase substantially”. In an effort to produce more forgiving high-BC bullets, Bryan Litz has developed a hybrid tangent/secant bullet shape. This is explained in the illustration below.
Story sourced by Edlongrange.
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The big news at Berger Bullets for 2011 is the Hybrid. No, Walt isn’t switching to a Prius… but Berger IS committing to the dual-shape hybrid design for a full range of calibers. The hybrid design combines a secant ogive (VLD-style) profile in the front of the bullet, with a tangent profile further back. This gives bullets the high BC of the VLD-style bullets, but the tangent section makes the bullets less sensitive to small variations in seating depth. The tangent ogive is a more gentle curve. Tangent ogive bullets, generally speaking, are more “forgiving” or easier to tune. They also will stay in tune better as a barrel throat erodes.
What Berger has done with the hybrid bullet is put an easy-tuning geometry on the part of the bullet that actually engages the rifling, while using a more streamlined front end for improved ballistics. This hybrid design was introduced in 2010 with hybrid 7mm and .338 bullets. Both new hybrid designs proved very successful. The hybrid designs were developed with significant design input from Bryan Litz, Berger’s ballistician. Before Bryan signed on with Berger, he literally worked as a rocket scientist, so he knows something about low-drag shapes. In the video below, Bryan explains why Berger will introduced more hybrid bullets in more calibers, in the months ahead. Bryan also talks about other products Berger has in the works, including its much-awaited reloading manual.
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Berger Bullets has just released its new .338-caliber “hybrid” bullet, Berger’s first-ever projectile larger than .30 caliber. The new bullet has a very high ballistic coefficient (BC): 0.891 under the G1 model, and 0.455 under the newer G7 standard for boat-tail bullets. That high BC should translate into exceptional long-range performance. According to Berger, the BC of the new Berger .338 bullet BC is roughly 14% better than the BCs of other .338-caliber 300gr offerings from Sierra and Lapua. This claim is supported by testing done on all three bullets and published in a detailed Bullet Comparison Report (PDF). The new .338 Hybrid bullets will be sold in 50-count and 250-count boxes. To order, call Berger’s Tech-Line, (714) 447-5458.
The key design feature of the new .338 bullet is its hybrid ogive, i.e. a shape that combines both tangent and secant geometry. A tangent ogive meets the bearing surface very smoothly, whereas a secant ogive has an abrupt juncture with the bearing surface. The figure below shows the geometric differences between a tangent and a secant ogive, as well as the strengths and weaknesses of each.
Practical Considerations — Load Length and Twist Rate
The superior ballistic performance of the 300gr Hybrid .338 is primarily due to the very long ogive and boat tail. However, that super-long bullet length can create some issues. Berger’s new .338 Hybrid bullets are so long that loaded rounds may not fit some magazines comfortably, unless you deep-seat the bullets, which cuts down on usable case capacity. If your loaded rounds with the new .338s are too long for your magazine, single-feeding is recommended. In addition, and this is IMPORTANT, to get optimal performance with the new bullets, you may want to extend the throat in your chamber. This can be done relatively easily by a competent gunsmith using a throating reamer. We caution, however, once the throat is pushed out, you can’t go back to a shorter throat without setting back the entire barrel.
The new .338 Hybrid bullets should stabilize well with a 1:10″ twist at the velocities achievable with popular .338 magnum cartridges. However, according to Bryan Litz, Berger’s Ballistician, at extreme long ranges (beyond one mile), as the .388 bullet goes trans-sonic, it may need more spin. As the bullet slows down into the trans-sonic range, extra stability is required — something you get by spinning the bullet faster. So, for those guys planning to shoot at one mile or beyond, Berger recommends a faster twist-rate. The faster twist provides more spin-stabilization at very long ranges. But for 1000-yard shooting, you don’t need to be concerned about trans-sonic stability. As Bryan explains: “So as long as you keep your shots under 1 mile, the 1:10″ twist is plenty adequate.”
Berger Bullets Video Update (Eric Stecker talks about the new .338 Hybrid and other matters.)
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In the 
