A Novel Armor-Piercing (AP) Projectile Design

Illustrated by the .408 CheyTac® Caliber

A novel armor-piercing projectile design with a tungsten carbide penetrator is described (US Patent 7,520,224 B2). For testing the novel design, a 40 caliber was selected in the .408 CheyTac® configuration. The new armor-piercing cartridge was tested against steel and titanium armor and it outperformed .50 AP (Black Tip [M2] and Silver Tip [M8]) under identical conditions. It did not outperform the .50 SLAP (M903) and there is some evidence that the .50 SLAP might have better perforation properties, but it lacks in accuracy with a normal .50 caliber barrel thus requiring a special barrel to achieve its best accuracy; the latter configuration was used in this investigation. Due to the .50 caliber cartridge’s heavier weight, the heavier weight of its firing platform, and less accuracy with normal and SLAP barrels, it is argued here that the .408 CheyTac® AP will make a better tactical cartridge on the battlefield.

The origin of the armor-piercing cartridge can be traced back to the 11mm Chassepot in 1866. This cartridge was linen-wrapped with a steel tip point projectile and used in a needle fire-breech loader.

Generally, the modern small arms armor-piercing projectile is made of two components: an outer jacket of copper alloy soft enough to be engraved by the barrel’s rifling and an inner core made up of a highly dense material such as tungsten carbide or depleted uranium. Other core (penetrator) materials have been used such as hardened tool steel but by in large, high-performance cores (penetrators) have been made of depleted uranium and tungsten carbide.

An examination of small arms, non-sabot armor piercing projectile designs (non-explosive) since 1945 found in the U. S. Patent and Trademark Office reviews a variety of designs (1, for representative patents). The designs vary but the common theme is an outer jacket and an inner penetrator (core).

A variation to the standard armor-piercing cartridge is the Armor Piercing Discarding Sabot (APDS) and the Saboted Light Armor Penetrator (SLAP). The term SLAP is used for calibers less than 20mm. The cartridge is made up of two components. The first is the armor-piercing projectile. This consists of a sub-caliber projectile (called a flechette, dart, or penetrator) often made of tungsten carbide or depleted uranium. The outer (sabot) is a plastic or some other non-metallic material.

Immediately upon leaving the muzzle, the sabot is stripped from the cartridge by centrifugal force and to a lesser extent air resistance leaving the penetrator free of the sabot to traverse toward the target. The advantage of the sabot armor-piercing cartridge over the non-sabot armor-piercing cartridge is greater velocity. The disadvantage is less long-distance accuracy.

Whether the cartridge is non-sabot or sabot, the constant is the penetrator. With the non-sabot, the outer surface is a copper jacket alloy and with the sabot, the outer surface is a non-metallic material.

Depleted uranium penetrators are currently restricted to only a few medium arms calibers due to indications of potential health risks to those handling the cartridges and as a result, more than likely will be phased out with time. A number of studies suggest that increased cancers and other abnormalities seen in the first Gulf war were due to the use of depleted uranium penetrators and were evident in the conflict in Afghanistan and in Iraq. Tungsten carbide displays better perforation properties than other penetrator materials and is a safe choice when contrasted to depleted uranium, but does not exhibit depleted uranium’s density and thus comes in second in performance.

In order to achieve the performance of depleted uranium penetrators, the military has been forced to use armor-piercing projectiles of higher calibers with tungsten carbide and steel penetrators. This results in increased weight, not only to the soldier carrying the cartridges but also to the transport of these cartridges to the battlefield, thus leading to higher transportation costs and restricted mobility on the battlefield.

One approach is to find a substitute material to replace depleted uranium that has the same or better properties. As a result, a search is ongoing in the field of Nanotechnologies. Here focus is directed to changing the molecular structures of steels and steel alloys to assume new properties, in some cases ideal for projectile penetrators. NanoSteel™ and Liquidmetal® are two such examples. Even though extensive studies have not as yet led to new metals and metal alloys, Liquidmetal® recently received a grant from the US military to develop a new metal alloy for projectile penetrators; these will replace depleted uranium.

It is not clear as to when Nanotechnologies will be successful in finding new penetrator materials with ideal properties. A second approach is to find new armor-piercing designs that use tungsten carbide as penetrator material. The second approach is to improve the use of tungsten carbide designs without going to increased weights.

We developed a new design using tungsten carbide as a penetrator that is superior to existing military armor-piercing cartridges of larger caliber (Figure 1). This new design should be able to take advantage of new penetrator materials as they are developed. Hypothetically, the design should be applicable up to 20 mm sized-projectiles even though testing has not been conducted in a caliber greater than 0.408 (10.4 mm).

Penetration vs. Perforation

The interaction of a penetrator with armor is divided into three phases. The first phase is initial impact resulting in the generation of stress waves within the armor, which leads to increased stress. Stress waves and levels are critical to initiate penetration. Shortly after impact, the projectile exhibits a radial tensile stress with the striking end of penetrator’s nose flattening radially while pushing into the target.

This is followed by the second phase where either or both the armor and penetrator behave as an imperfect fluid. Failure occurs in those regions where pressures involved are higher than the yield strength of the armor. The back of the penetrator travels faster than its front resulting in the projectile undergoing deformation. The projectile erodes backwards toward its base adding its material to the armor’s forming crater wall as well as to its depleting self. The projectile disappears as its projectile’s shape.

The third phase is the perforation whose characteristics vary depending upon the type of armor. What is known is that armor failure is caused by an interaction of a variety of mechanisms with no one superceding any other. Common mechanisms identified by terminal ballistic scientists (for review summary, see 1) include fracture, radial fracture, spalling, scabbing, plugging, front or rear petalling, or fragmentation and ductile hole enlargement (Figure 2).

Types of Armor

Armor can be found in specific types of steel alloys, ceramics, aluminum alloys and recently titanium alloys.

Armor steel is found commercially from various firms. Each claims certain properties that best defeat or resist incoming projectiles. Several common examples include Omega Armor and Wearalloy® Armor. The major disadvantage to steel armor is weight. Weight has always been a major concern to the military. As a result, a substitute for armor steel has been a focus leading to ceramics, aluminum and titanium armors.

Recent reports suggest that titanium alloy’s ballistics performance is an attractive alternative to steel alloys. For example, it has been reported that Ti-6Al-4V and Ti-6Al-4V ELI provides better projectile resistance than certain steel or aluminum alloys. Most of the studies deal with projectiles of calibers 15mm plus and are associated with attacks on armored vehicles.

Historically, weldable aluminum armor has been used for the protection against high explosive shell fragments. Generally, its resistance to incoming projectiles is less than steel. Exceptions exist. The advantages are the savings in weight and the lack of corrosion.

Ceramic armor normally is found in a tile configuration. It defeats armor-piercing projectiles by breaking up the projectile in the ceramic material and absorbing the fragments’ energies in the plates, which back the ceramic tiles. During this process, damage is produced in the ceramic armor. Multiple hits in the same area are usually controlled by the size of the tile. Stress from one tile to the next is minimized.

Even though useful to examine all types of armor in establishing the physical characteristics of a newly designed armor-piercing projectile, it seems reasonable to use armor steel for such studies. Many of the effects on armor steel can be readily compared to other types of armor material, but it may be difficult to compare results from a non-steel armor back to steel. As a result, armor steel was used in this study, specifically Wearalloy armor or AR 550.

A new type of titanium armor from Allegheny Technologies came available to us during this study. The armor was made up of laminated titanium plates. Even though an extensive study was not conducted, limited results are presented.

.408 CheyTac® Armor Piercing Cartridge

Most common armor-piercing cartridges are those with a copper jacketed projectile surrounding a penetrator. Rather than a copper jacket, the .408 CheyTac® armor-piercing cartridge starts its manufacturing with a solid alloy projectile, lathe-cut from a solid proprioritary metal rod. Initial projectiles are made in two weights: .305gr and 419gr. At this stage of manufacturing, the solid design gives the projectile some armor piercing capabilities over what would be found in a lead-core copper jacketed non-armor piercing projectile. Thus, solid projectiles start with an advantage leading to a much more efficient final armor-piercing projectile.

Working with PRODAS software, projectiles were designed so that the linear drag on a projectile is matched to its rotational drag. In other words, forward rate of deceleration and an axial rate of deceleration are balanced. The gyroscopic stability remains constant resulting in the projectile remaining on its original trajectory path. This “Balance Flight” projectile design is protected by our patent (6,629,669).

Materials And Methods

The first step was to design an armor-piercing projectile with a penetrator inside of the projectile (Figure 3).

The most common materials used for penetrators in armor piercing cartridges are steel and tungsten carbide. Tungsten carbide was finally selected, but other materials tested included: boron carbide, hardened tool steel, oil hardened drill rod, and NanoSteel™. Results of these materials are not presented here.

The 305gr and the 419gr projectiles were selected for conversion to armor-piercing states. To approach Balance Flight characteristics of an armor-piercing projectile, tungsten carbide penetrators were made with a consistent weight and were inserted from the base directly in the center of the projectile. The base was sealed with a cap of consistent weight. Diameter, length of the penetrator as well as the depth of the penetrator into the projectile are not given here but instead, are found in our patent (7,520,224).

High precision methods were utilized in order to insure that the gyroscopic stability of the projectile during flight remains constant, which result in it not deviating from its original trajectory path. The goal was to approach “Balance Flight” characteristics.

The logic behind the design is the following. The material selected for the outer solid was to insure that the penetrator remains in a solid state as long as possible while penetrating the armor target. This is achieved after the projectile impacts the armor target when the outer solid, in the process of penetrating the armor target, turns to an imperfect fluid before the inner penetrator turns to an imperfect fluid. At the same time, the material for the outer core must have the properties to engrave to the barrel’s rifling.

Quality control of armor-piercing projectile’s accuracy was measured against a benchmark of one MOA or better before hitting the target. Goal was to made armor-piercing projectiles that would achieve one MOA or better out to 500 yards.

Several different types of armor steel are commercially available. For this study WearAlloy® AR 550 plates were selected with thickness of 0.375-, 0.5-, 0.75- and 1.0-inch and were placed at distances of 100, 175, 500 and 650 yards.

During the experimental phase of this project, we received some titanium armor plates made by Allegheny Technologies. These were not under our control during testing other than shooting at them. Tests were run at 100, 200 and 300 yards up to 1-inch of laminated plates.

All testing was conducted at Arco, Idaho with an elevation of 5325 feet. Mean muzzle velocities for the following:

305gr ball = 3250 fps
419gr ball = 2850 fps
305gr (370gr) AP = 3125 fps
419gr (490gr) AP = 2650 fps

Finally, .50 AP (Black Tip [M2]), .50 AP Incendiary (Silver Tip [M8]) and .50 SLAP (M903) cartridges were used as controls. M2 weight 1812 plus/minus 73gr, M8 weights 2910 plus/minus 30gr (4), and M903 weights 1466gr. The .50 SLAP (M903) is not accurate with a regular SLAP barrel thus a barrel designed for the SLAP was used (twist of 1X22).

Result & Discussion

I. Summary of Results with Armor

Actions of projectiles against armor steel targets are summarized in Table I. The 305gr (370gr) AP cartridge with a MV of 3125 fps out performed the 419gr (490gr) AP cartridge with a MV of 2650 fps.

The conclusion to this phase of the study is that .408 CheyTac® AP projectile perforates 1″ WearAlloy 550 armor steel at 100 yards and 3/8″ WearAlloy 550 armor steel at 500 yards with 1 MOA or better before hitting the armor target. It perforates 3/8″ WearAlloy 550 armor steel at distances greater than 500 yards with MOAs greater than 1 before hitting the armor target. The .50 Armor-Piercing projectile (Black Tip) and .50 Armor-Piercing Incinerary (Silver Tip) projectiles with their steel penetrators failed to achieve these results under the same conditions.

In addition, it perforates 1” Allegheny Technologies 425 armor titanium up to 300 yards with 1 MOA or better before hitting the armor target. We have yet to run the tests to determine where 3/8” 425 armor titanium stops the .408 CheyTac® AP projectile, but our “estimate” is approximately 600 yards. We were told by a representative that .50 Armor-Piercing projectile (Black Tip) defeats the 1” 425 armor titanium at 50 yards and less but not greater than 50 yards.

II. Accuracy

The armor-piercing projectile design demonstrates sub MOA out to 500 yards. Tests were restricted to this distance and we have nothing to report beyond 500 yards except sub MOA groups were not achieved. Our guess is that the gyroscopic rotation’s ability to stabilize projectiles lessened as we have been able to obtain sub MOA out to 1,700 yards with standard cartridges. We are working to achieve sub MOA out to 1,000 yards with these armor-piercing projectiles.

III. Mechanism of Action on Steel Armor

Analyses of the impact sites generated adequate data to determine whether the logic behind the predicted mechanisms of action was totally, partially or not correct. The prediction is that while the outer solid is in an imperfect fluid state it serves as a viscous track facilitating the penetration of the solid penetrator. This increases the penetration of the penetrator deeper into the armor target than if the viscous track was not present.

In addition, this along with a very hard material making up the outer solid delays the penetrator from readily turning into an imperfect fluid. During penetration, the armor target at the site of impact also turns to an imperfect fluid. Finally, the penetrator continues to penetrate until all of it turns to an imperfect fluid. The end of this stage, the penetrator is no longer evident as a penetrator. Instead, the penetrator is found melted on the penetration walls as well as the bottoms of the indentations of the armor plate in those cases where perforation was not achieved.

In sum, if the penetrator can remain as a solid long enough, it will perforate the armored target. The outer solid is the key to insure that the penetrator has not expended all of its velocity; i.e. it first penetrates the armor giving the penetrator a head start and second provides a viscous track to reduce friction between the penetrator and the armor. This is the reason that the design outperforms all existing military AP designs.

Figure 4 shows 305gr and 419gr projectile penetration in 0.75-inch armor plate. Note that both displayed penetration with the 305gr projectile being the greatest. It almost defeated the plate. Also note that the projectiles had melted and had coated the walls of the craters.

Using that the interactions of armor-piercing projectiles with armor are divided into three phases as standards against our morphological observations, the greatest variability was found with the third phase or the perforation phase. Our data supports what terminal ballistic scientists have reported in the literature (for a review summary, see 1).

Figure 5 shows two images: front and back of 1-inch armor. The back shows a large portion blown out with a plug (star) about ready to fall to the ground. Contrast this to Figure 6 that shows the cross-section of armor (star) and the penetrator not quite through the armor. A reasonable conclusion is that with the latter, the penetrator ran out of kinetic energy while with the former, more than enough kinetic energy was available. Were the differences in the two different cartridges; i.e., one loaded hotter than the other or was the difference in the steel; i.e., armor steel plate is not homogeneous in its properties from one plate to another? Clearly the answer cannot be found in this study.

The smallest variability was found with phases 1 and 2. Note in Figure 7 and Figure 5 top that outer solid alloy has melted and a portion is extruded from the hole to the surface of the plate. This is the common appearance; however, there are examples where the solid alloy did not melt and extrude to the surface of the plate (Figure 8). Here, an examination of inside the hole reveals melted outer solid.

Figure 6 supports the hypothesis that the outer solid delays the penetrator from turning into an imperfect fluid as it penetrates through the armor. Here the tip of the penetrator is protruding from the backside of the armor plate and appears to be intact. Note that there is not melted outer solid on this side. All of this is found in the hole as seen from the front side of the armor plate.

However, variations can be found here. In a few examples where the penetrator did not perforate the armor plate, it was found as the base of the hole clearly showing signs that it melted.

With some variability, we believe we have enough evidence to support our hypothesis that due to the unique design of our armor-piercing projectile, the outer solid has some penetration characteristics. This facilitates penetration (direct evidence). In addition, when the outer solid turns to an imperfect fluid, this may serve as a viscous track adding additional facilitation penetration to the penetrators (indirect evidence). And, it delays the penetrator from turning to an imperfect fluid thus facilitating its defeating the armor (direct evidence).

Figure 9 contrasts the performance of the .408 AP projectile against that of the .50 AP (Silver) projectile. The .408 AP projectile perforates 1-inch armor steel while the .50 AP does not.

The new design in the .408 CheyTac® AP caliber will be called the .408 CheyTac® AP (Black Tip).

In order to determine that the 1-inch armor steel plate could be penetrated by another type of cartridge, .50 SLAP defeated this armor (Figure 10).

IV. Mechanism of Action on Titanium Armor

In closing, we did examine Allegheny Technologies (AT) titanium armor. This is presented as plates enclosed in an armor case (Figure 11). We found that our armor-piercing projectile would defeat 1-inch up to 300 yards (Figure 12). The AT representative told us that .50 AP would defeat at 50 yards but not at greater distances. We have no first hand experience to support or not support this statement. We were not in charge of the shooting conditions. One must take our results with some caution as we don’t know the state of this armor; i.e., experimental, on the market etc.

Significance

The .408 CheyTac® cartridge outperforms the .50 Ball (M2) and the Raufoss (MK 211) in all ballistic categories including kinetic energy past 400 yards (3).

Even though we did not test the limits of the .408 CheyTac® AP, it appears the .50 SLAP may outperform it in defeating armor, based on contrasting the appearances of the holes in the 1-inch armor plates. This was not a surprise. However, it was a surprise that the .50 AP (Black Tip) and .50 AP Incendiary (Silver Tip) did not outperform the .408 CheyTac® AP.

Even though penetration and perforation advantages may go to the .50 SLAP, the .408 CheyTac® AP has several tactical advantages on the battlefield. For example, it weighs 656gr in contrast to .50 SLAP weight of 1466gr. Generally, the .408 CheyTac® rifle’s weight is less than that of the .50 rifle. In addition, the .408 CheyTac® AP is accurate, maintaining 1 MOA or better up to 500 yards while the .50 SLAP accuracy is elusive unless a SLAP barrel is used. Going from a regular barrel to a SLAP barrel on the battlefield is not advantageous. In our hands, we had problems hitting a 24-inch by 24-inch targets with this cartridge at 500 yards using SLAP barrels.

So with a savings in weight in both ammo and firing platforms and greater accuracy, the .408 CheyTac® AP should turn out to be more advantageous than the .50 SLAP on many battlefield encounters. Add this to the fact that the cartridge outperforms the .50 AP (Black Tip; ~1812gr) and .50 AP Incendiary (Silver Tip; ~2910gr) in accuracy, armor penetration and weight savings, we feel that this new AP cartridge can make a major contribution to our military as well as to Homeland Security.

Production of these cartridges will start shortly.

John D. Taylor, Ph.D.
Founder & Co-Owner
Chief Technical Advisor, CheyTac® USA,
*US Patent 7,520,224

Acknowledgement: Thanks go to Dave Durham for his contributions to this study.


References

  1. U.S. Patents: 3,599,573; 3,782,287; 4,044,679; 4,108,073; 4,619,203, 4,704,968; 4,878,434; 5,009,166; 5,794,320; 6,085,661; 6,115,894; 6,119,600; 6,158,351; 6,286,433; 6,374,743; 6,581,522; and 6,973,879.
  2. Smith, C. J. M. and P. R. Haslam. 1982. Small Arms & Cannons. Brassey’s Publishers (Pergomon Group), Oxford.
  3. Taylor, J. D. 2002. .408 Cheyenne Tactical™ — A Novel 2,000-Meter Tactical Cartridge. Part III. Precision Shooting, Vol. 50, No. 2, pp. 39-64.
  4. Barnes, F. C. 2003. Cartridges of the World, 10th Ed. Krause Publications, WI.

APProjectileDesign_Fig1

 

Figure 1. The .408 CheyTac® 419gr cartridge is on the right. To the left is the .408 CheyTac® AP cartridge with its painted Black Tip (arrow). The armor-piercing projectile was made from a 305gr solid projectile plus a tungsten carbide penetrator with a final weight of 370grs.

APProjectileDesign_Fig2

 

Figure 2. Summary of proposed projectile armor interactions (2). Plugging (d) was evident in this study.

APProjectileDesign_Fig3

 

Figure 3. A general design of the armor-piercing projectile. Star represents the penetrators. Cap is located at the base. The remainder is the outer solid alloy of the projectile.

APProjectileDesign_Fig4

 

Figure 4. A contrast between 305gr and 419gr solid alloy projectiles against 0.75-inch armor steel at 100 yards. The 305gr projectile was close to defeating the plate. Clearly both weight projectiles have armor-piercing ability without an internal penetrator.

APProjectileDesign_Fig5

 

Figure 5. Front and backsides of 1-inch armor steel with perforation hole. Top. Front side. Note where the solid alloy of the projectile extruded out of the penetration hole back onto the plate (arrow). Bottom. Backside. Note the opening to the front side (arrow). A plug of armor is close to falling off the armor (star). In fact, after this picture was taken the plug did fall off. This is a good example of a penetrator perforation.

APProjectileDesign_Fig6

Figure 6. A side view of a cross-section of an armor steel plate (star) and a penetrator (arrow) that has not quite perforated the plate. Note that the surface of the armor plate is free of melted outer solid alloy of the projectile. This is found on the front side of the plate. The plate is slightly out of focus in order to focus on the penetrator.

APProjectileDesign_Fig7

Figure 7. The outer solid alloy of the projectile has melted with a portion of it extruding from the hole to the surface of the armor plate (arrow).

APProjectileDesign_Fig8

Figure 8. Two infrequent examples where the outer solid alloy of the projectiles did not extrude from the two holes to the surface of the armor plate. Note that the edges of the holes are sharp (arrow).

APProjectileDesign_Fig9

Figure 9. Top, .408 CheyTac® AP perforates 1-inch armor steel at 100 yards. Insert, back of armor plate showing hole. Bottom, .50 AP (Silver). Back of armor plate displays no perforation (not shown).

APProjectileDesign_Fig10

Figure 10. .50 SLAP at 100 yards. Front and backsides of 1-inch armor steel plate with a perforation hole. Note that the edge of the hole is sharp – no residue such found with the outer solid alloy of the .408 CheyTac® AP projectile.

APProjectileDesign_Fig11

Figure 11. Layers of titanium armor enclosed in an armor case.

APProjectileDesign_Fig12

Figure 12. One-inch titanium armor. .408 CheyTac® ball did not penetrate but .408 CheyTac® AP penetrated at 100, 200 and 300 yards.


Table I
Results (Summary)

100 yds, WearAlloy ½” AR 550 armor steel
305gr ball @ 90 degrees – perforated*
419gr ball @ 90 degrees — perforated
305gr (370gr) AP @ 90 degrees – perforated*
419gr (490gr) AP @ 90 degrees – perforated

*The 305gr displayed a sharper cut in the armor over the 419gr

100 yds, WearAlloy ¾” AR 550 armor steel
305gr ball @ 90 degrees – penetrated but did not perforate
419gr ball @ 90 degrees – penetrated but did not perforate
305gr (370gr) AP @ 90 degrees – perforated
419gr (490gr) AP @ 90 degrees – perforated

100 yds, WearAlloy 1” AR 550 armor steel
305gr ball @ 90 degrees – penetrated but did not perforate
419gr ball @ 90 degrees – penetrated but did not perforate
305gr (370gr) AP @ 90 degrees – perforated*
419gr (490gr) AP @ 90 degrees – penetrate but did not perforate
50 AP Silver and Black Tip @ 90 degrees – penetrated but did not perforate**
.50 SLAP – perforated

*Some perforation was encountered, which can be described as plugging. Perforation was not consistent.
** Those 305gr (370gr) AP and 419 (490gr) that did not penetrate went deeper into the armor than the .50 AP Silver and Black Tips. The 305gr (370gr) AP went deeper than the 419gr (490gr) projectiles.


 

500 yds, WearAlloy 3/8” AR 550 armor steel
305gr ball @ 90 degrees – penetrated but did not perforate
419gr ball @ 90 degrees – penetrated but did not perforate
305gr (370gr) AP @ 90 degrees – perforated
419gr (490gr) AP @ 90 degrees – perforated

650 yds, WearAlloy 3/8” AR 550 armor steel
419gr ball @ 90 degrees – penetrated but did not perforate
305gr (370gr) AP @ 90 degrees – perforated but went beyond 1 MOA

175 yds, WearAlloy ¾” AR 550 armor steel
419gr ball @ 90 degrees – penetrated but did not perforate
419gr (490gr) AP @ 45 degree angel – 70 % penetration
419gr (490gr) AP @ close to 0 degree angle – 40% penetration
419gr (490gr) AP @ 90 degrees – 90%

Sample sizes ranged from 1 to 5