Cased Telescoped Ammunition: The Next Step in Ammo Evolution?


Comparison of traditional NATO ammo with smaller CTA rounds that are more powerful.

The U.S. Army is on the hunt for a new small arms weapon system to replace its current rifles and light/medium machine guns. Currently they have contracted five companies to provide a prototype for the Next Generation Squad Automatic Rifle (NGSAR). At least one company, Textron Systems, will be fielding a prototype machine gun that fires cased telescoped ammunition (CTA) (South, Todd, “The Army’s Next Machine Gun Could Fire Caseless Ammo—and One of These Companies Might Build It,” Army Times, July 12, 2018… If Textron with CTA is awarded the contract to produce the Army’s next light/medium machine gun, it would create a huge impact on the future of small arms by being one of the first big changes to ammunition since the invention of the current brass casings. Why is there a need for new bullet technologies? As of late, new fluid body armor technology has been developed that could make most battlefield rounds obsolete (Caughill, Patrick, “New Ultra Lightweight ‘Fluid Armor’ Can Stop a .44 Magnum Bullet,” Futurism, May 17, 2017, Many of these new protective light armors could render most modern rounds ineffective if there is not a next-generation of ammo developed.

What Exactly is CTA?

CTA is another form of cartridge. The “telescoped” aspect means the bullet is partially/completely enveloped by the propellant charge. In the case of the ammunition being fielded by Textron, it has a “straight-wall polymer case with a centrally located primer in its base … The projectile is surrounded by propellant up to its cannelure. The case is open at the front with the projectile nose visible. A single groove runs around the circumference of the forward part of the case” (Fortier, David, “Telescoped Ammunition Might Be the Future of Cartridges,” Rifle Shooter Magazine. Aug. 29, 2018… CTA retains all the same parts of current ammunition but adds in polymer to modify its position. The idea behind this is to get a lighter cartridge that is a bigger and more powerful projectile with the same weight as a smaller brass counterpart.

Textron Systems claims that CTA has many advantages over conventional ammunition, including a significant reduction in weight. It claims to be able to field a medium machine gun, firing the CTA equivalent of 7.62 NATO with 600 rounds, at only 3 pounds heavier than the current M249 light machine gun firing 5.56 NATO with 600 rounds (Shipley, Paul A., Benjamin T. Cole (AAI Corporation, Textron Systems Unmanned Systems) and Kori Phillips (U.S. Army ARDEC, Joint Service Small Arms Program). Cased Telescoped Small Arms Systems. NDIA Joint Armaments Conference: Textron Systems, May 2014). It also claims that the new weapon with CTA has better reliability, is easier to maintain and has less felt recoil and improved accuracy. While all those are just claims, the U.S. Army will definitely put every single one to the test with thousands of rounds each. And if it turns out that Textron’s claims run true then CTA will change the face of small arms as we know it.

History of CTA

The idea for improvement and innovation over current ammunition has been around for a long time. From electrically/magnetically fired projectiles, to CTA, to caseless ammunition, enormous amounts of money, time and research have been spent on trying to figure out the next step in the evolution of ammunition. For a time, it seemed as though caseless telescoped ammunition would take the forefront for new innovation, and in 1977, the U.S. Air Force was even granted a patent to this caseless ammunition (Harold O. Evans, Caseless Ammunition Round with Spin Stabilized Metal Flechette and Disintegrating Sabot. U.S. Patent US4015527A, filed March 10, 1976, and issued Apr. 5, 1977).

Caseless ammunition is very similar to CTA, but instead of a polymer case, its case is made from solid propellant, making the case and propellant singular. But it seems that the challenges of producing caseless ammo were never completely overcome, and CTA has taken the lead as the next step in ammunition development. Since its inception in an Air Force laboratory in 1954, CTA did not look like it was fairing much better though, and in fact, CTA has been wrought with issues over the years. In 1995, a report from the Inspector General stated “$213 million [spent] over 41 years has not resulted in a viable weapon system” (U.S. Department of Defense/Defense Technical Information Center. Office of the Inspector General. “DOD Cased Telescoped Ammunition and Gun Technology Program,” by Robert J. Liberman. Report No. 96-164. June 14, 1996). But the report countered the lack of progress by saying the research being conducted was important, and if several major issues could be resolved, then CTA could provide a new lethal advantage to the battlefield. It seems only in the past 2 decades since this report, have polymers become advanced enough to make CTA actually viable. But that does not mean that there are no issues that need to be resolved.

Differences in How Weapons Firing CTA Function

CTA, because of its differences, requires a new operating procedure with the bolt and receiver from current weapons. Two of the current machine guns the Army seeks to replace, the M249 SAW and the M240B/L, operate like all other guns have for the past century (FN. “FN® M249 SAW.” FN® America. The chamber and barrel are forged from one piece, the cartridge is pushed into the fixed chamber, fired and then the casing is extracted so the process can repeat and continue.

CTA is different in that “normal” extraction does not work with polymer casings. To get around this, a “swinging chamber” has been developed. How this works is a round is placed into the chamber in the open position. Then the chamber swings in line with the barrel for firing. After the round is fired the chamber rotates back into the load position. A new round is forced into the rear of the chamber, pushing the spent casing and any other debris out of the front of the chamber (McGregor, Captain I.A., “Telescoped Ammunition a Future—Lightweight Compact Ammunition?” The Canadian Army Journal, 12.2, No. Summer 2009, 75-81. This also helps keep the heat of the chamber low, so the polymer cases are not as likely to melt, which has presented issues in the past. The new firing system also allows for CTA rounds to be perfect cylinders, which simplifies manufacturing. Another difference is that cartridges are also linked together by a polymer chain instead of the traditional metal links that held belts of bullets together.

Design Considerations and Challenges

A big challenge in designing CTA is making a polymer casing that can withstand the high temperatures and contained explosion, in the firing of a round. A study done by the Armament Research, Development and Engineering Center put different polymers to the test and based on their criteria showed how different polymers failed and why they did so (U.S. Department of Defense/Defense Technical Information Center. Armament Research, Development and Engineering Center. “Alternative Case Material and Design,” by Jerry S. Chung, Frontier Performance Polymers Corporation and Lucian M. Sadowski, Project Engineer, ARDEC. Technical Report ARAEW-TR-05007. July 2003 to Oct. 2004). The lessons learned from this study have led to the polymer casings that Textron is fielding in their prototype.

Another issue arises in that CTA “not only reduces the volume available for the propellant charge but also places severe geometric constraints on both the distribution of the propellant and the location and functionality of the ignition system” (U.S. Department of Defense/Defense Technical Information Center. Army Research Laboratory. “Progress in Modeling Ignition in a Solid Propellant Charge for Telescoped Ammunition,” by Michael J. Nusca and Albert W. Horst/Weapons and Materials Research Directorate, ARL. Vol. ARL-TR-3673. Nov. 2005). This problem was addressed in a study by the Army Research Laboratory, in which they tested different solid propellants to find one that could produce more power with less volume while also being very consistent. They were unable to find a perfect match, but the results showed exactly what the perfect propellant would need to look like.

An article in Defense Technology Journal also pointed out that because the chamber is rotating and not fixed, every time it locks back into firing position, it will be aligned slightly differently. This results in more wear in the throat of the barrel and also reduced accuracy. The results from this experiment give an acceptable allowed error in how precise the chamber needs to lock every time to expect a certain accuracy (Corriveau, D., and C. Florin Petre, “Influence of Chamber Misalignment on Cased Telescoped (CT) Ammunition Accuracy,” Defence Technology, 12, No. 2 (Apr. 2016): 117-23. doi:10.1016/j.dt.2015.11.008). Companies can use this data to make sure they are precise enough in how much the chamber is allowed to slip-in-error between rounds.

                In the Journal of Mechanical Science and Technology, a different article showed how the barrel of a weapon reacted differently to CTA rounds being fired. The experiment illustrated the different kinds of shock caused by CTA relative to standard ammunition, showing how the barrel vibrations differ. From these findings, companies can see how the barrels are stressed and better choose the correct material and design of a barrel to properly handle CTA (Gimm, Hak In, Ki Up Cha and Chang Ki Cho, “Characterizations of Gun Barrel Vibrations of during [sic] Firing Based on Shock Response Analysis and Short-time Fourier Transform,” Journal of Mechanical Science and Technology, 26, No. 5 (May 2012): 1463-470. doi:10.1007/s12206-012-0335-5).

The rotating chamber of CTA also lets what would be propelling gasses escape, much like a revolver and the gasses that escape between the cylinder and the barrel. In a test performed by Mechanical Solutions, Inc. for the U.S. Department of Defense, different materials were tested to see how well they could make a seal between the chamber and the barrel (U.S. Department of Defense/Defense Technical Information Center. Mechanical Solutions, Inc./U.S. Army TACOM-ARDEC. “Cased Telescoped Ammunition Smart Seal Development,” by William J. Kelly and William D. Marscher. Vol. TR-81801. Sep. 5, 2002). Mechanical Solutions looked at the different properties and what has been used to create a seal in similar environments before. Another similar test was conducted by the Nanjing University of Science and Technology in China. Their findings showed a “sealing structure [that] has a good sealing performance and can solve the spherical transient high-pressure gas seal problem for the rotating chamber of the medium calibre CTA gun, and it is expected to offer a reference value to solve related problems in engineering” (Chen, Longmiao, Qiang Fu and Gui Lin, “Study on the Sealing Properties of the Sealing Structure for the Rotating Chamber of a Certain Cased Telescoped Ammunition Gun,” Computer Modelling & New Technologies, 18, No. 3 (March 1, 2014): 93-97.). These tests helped find the right seal to attain the least amount of propellant gas lost, thus making CTA more efficient to produce higher bullet velocities.

Why Is so Much Effort Being Put into CTA Anyway?

A question that should be considered: Is there really anything wrong with current ammunition and firearms? They are clearly proven and tested to be reliable and accurate for the last century; otherwise, a new ammo and/or firearm would have been already developed. Per Arvidsson from Small Arms Defense Journal argues that there really is no need to run away from the current ammunition, especially the 5.56. He claims that if countries want more lethal small arms, that better training is needed for security forces, not new weapons or ammo (Arvidsson, Per, “Is There a Problem with the Lethality of the 5.56 NATO Caliber?” Vol. 3, No. 1, Small Arms Defense Journal, Jan. 6, 2012.). This would certainly seem to be more cost efficient as 5.56 is streamlined across all of NATO already. Moving to CTA would mean huge upfront costs in terms of buying new weapons and converting ammunition factories to produce it (“The Case for Caseless Telescoped Ammunition,” Military News. YouTube. Nov. 25, 2017.). Yet, it seems the U.S. Army still wants more bang for less weight and is set on getting a bigger round than the little 5.56 (Keller, Jared, “The Army Is One Step Closer to a 6.8mm Next-Generation Rifle,” Task & Purpose, Oct. 8, 2018.). Such a decision for CTA usage would likely compel NATO countries to adapt as well.

Regardless, it really is all about the weight/power ratio. In the article, “The Soldier’s Heavy Load,” the author describes how dismounted soldiers’ mobility and effectiveness correlates to the amount of weight they have to carry (Fish, Lauren, and Paul Scharre, “The Soldier’s Heavy Load,” Center for a New American Security. Sep. 26, 2018.). Soldiers are physically limited on how much they can carry and at times have to sacrifice protection for mobility, or mobility for firepower, etc. Unfortunately, technology often increases weights, instead of decreases loads carried. Weapon to weapon, CTA can decrease the weight carried both in the firearm itself and the ammunition, proving advantageous because every pound counts when it is being put on a soldier (Tobias Lindner, Christoph Schulze, Sandra Woitge, Susanne Finze, Wolfram Mittelmeier and Rainer Bader, “The Effect of the Weight of Equipment on Muscle Activity of the Lower Extremity in Soldiers,” The Scientific World Journal, vol. 2012, Article ID 976513, 8 pages, 2012. And if for the same weight a soldier can carry more firepower, it also seems to be advantageous. This seems to be the reason why CTA is being considered so heavily.

But CTA is not the only way to reduce weight. A report filed by Major Steven Miskinis for the U.S. Army Command and General Staff College shows that an aluminum casing would weigh less than the polymer of a CTA counterpart, and aluminum is less flammable. His findings also show that aluminum would cost less, while CTA would be the same cost as current brass cased ammunition; although he does admit that CTA has a substantial advantage in corrosion resistance (U.S. Department of Defense/Defense Technical Information Center. U.S. Army Command and General Staff College. “Should the U.S. Army Adopt New 5.56mm Ammunition Cartridge Designs to Reduce Overall Ammunition Weight?” by Major Steven G. Miskinis, Jr. Fort Leavenworth, KS, June 2011. So why not just replace brass with aluminum? It seems that with aluminum being a cartridge case, it has a vital flaw of a “burn-through phenomenon” where the casing fails and, in the process, completely disables the weapon (U.S. Department of Defense/ Defense Technical Information Center. Frankford Arsenal. “An Analysis of 5,56mm Aluminum Cartridge Case Burn-Through Phenomenon,” by Walther H. Squire and Reed E. Donnard, Jan. 1972. AD0750379). If this can be fixed it may be a better alternative, but so far the emphasis on CTA would hint at this not being an easily fixable flaw.

Bottom Line

CTA has not been perfected. While being first envisioned in 1954, CTA has seen great advancements in the last decade. Testing for CTA must continue finding faults, while providing cost-effective solutions. If CTA can live up to the claims given to it by Textron and others, it seems that the future of small arms lies within it. If not, it is just one more idea scrapped either for good or until technology can advance to the point to make it viable. Regardless of its failure or success, the continuous process for something that weighs less, hits harder and is cheaper to manufacture will continue. But for now, all one can do is sit back and watch where CTA goes, especially with an enormous U.S. Army contract on the line and with adversaries developing new armor technologies to protect against current NATO rounds.

Nathan Fairhurst is a Research Assistant in the Department of Military & Strategic Studies, U.S. Air Force Academy. Dr. Jahara Matisek (Major, U.S. Air Force) is an Assistant Professor in the Department of Military & Strategic Studies, and a U.S. Air Force Academy Non-Resident Fellow, Modern War Institute, West Point, U.S. Military Academy.