INTERVIEW with Kori Phillips, Program Officer for LSAT and CTSAS, Part 3: Development of 6.5mm CT

    Kori Phillips holds some linked 5.56mm CT ammunition side by side with a belt of 5.56mm brass-cased dummy ammunition at media day at Picatinny Arsenal on May 4, 2015. Image credit: David Vergun, public domain

    Not long after SHOT Show, I got the chance to interview Mrs. Kori Phillips, former program officer for the Army’s Lightweight Small Arms Technologies (LSAT) program, and current program officer for the Cased Telescoped Small Arms Systems (CTSAS) program. We talked at length about both programs, the technology they developed, and the state of lightweight ammunition today. The interview, which spans fifty-five questions, will be broken up into three sections, each covering questions about different aspects of the program, to be published monthly once each in March, April, and May-wait, hold on,

    Our Dear Leader Steve has approved a weekly timeline for the interview, instead of a monthly one. That means we’ll be finishing up today! Hooray!

    If you haven’t seen the previous two installments, you can read them here and here.

    Before we begin, I would like to take a moment to thank Kori and Frank for taking the time to speak with me. They were very patient with me and did not hesitate to answer any of my questions.

    Now, we’ve got a lot to get through! My questions are labeled with a bold “TFB“, while Kori’s answers are labeled with a bold “KP“:


    TFB: Can you tell me about the caliber study that you did?

    KP: We had this notion that there had to be a better bullet out there. And I know that the Army is undertaking a huge project, but it’s not just about the bullet, it’s about the weapon and how you use it and how many rounds of ammunition you are carrying. We stopped at a very simple answer, we had been talking to the AMU, specifically Troy Lawton, and he had an idea for a better bullet. For CT, which isn’t constrained by old weapon configurations, why are we shooting old bullets? Why not use something that shoots better? So it was very quick, only took about six months. We looked at different shapes, different sizes and weight. It came down to the maximum amount of range and effect you could get out of a bullet at the minimum weight. We were looking at where those two lines on the graph crossed, and that’s where we wanted to be. It was very complicated, it was like a four dimensional matrix. It became very obvious early on that the long, low-drag bullet was going to address a lot of the questions we had. You get this range automatically, you don’t need to make it fly faster, or make it heavier, it automatically flies further because it has low drag. And we thought if we could amp up the velocity a little bit, so we can give it more punch. The advantage we have is that we can design a cartridge case around the bullet, we don’t have to try to fit the bullet into an existing cartridge case. I always caveat our caliber study that this is only for cased telescoped.


    TFB: Originally, LSAT focused on a 5.56mm weapon, but now the focus with CTSAS appears to be a 6.5mm weapon. How did this change come about? Was it a decision from the Infantry School, or an internal development by CTSAS? Is the 6.5mm now the focus of CTSAS, or a side project?

    KP: Based on the success of the original 5.56mm CT system, we were given funding from the Army to pursue a Medium Machine Gun (typically 7.62mm) and a Carbine. The 6.5mm ammunition came about as a result of an optimization study that was done strictly for the CT configuration. Both new weapon systems can be used with either a 7.62mm CT cartridge or the 6.5mm CT cartridge.


    Original caption: “Kori Phillips, an ARDEC systems management engineer, talks to Sgt. Jason Reed about the chamber of the lighter version of the M249 machine gun.” Image credit: Eric Kowal, RDECOM. Public domain.


    TFB: Fort Benning appears to have issued a 1,200m effective range requirement (this appears on some slides in NDIA presentations). What can you tell me about this requirement? How did this requirement affect the program?

    KP: I really can’t speak to any requirement generated by Ft. Benning, you’ll have to go to them for more information. The 1,200 m shown in my NDIA slides is just a “rule of thumb” for medium caliber energy measurement, and is not related to an operational requirement.


    TFB: The 6.5mm CT so far appears to be slated for an LMG and a carbine. This seems to indicate that CTSAS is designing for a one-round Army, replacing all 5.56mm and 7.62mm weapons with the new 6.5mm CT weapons. Is this the case? Why was this decision made, if so?

    KP: No decision has been made – we are providing the 6.5mm so that soldiers and leadership can evaluate it against the 5.56mm and the 7.62mm. It will be fired from the CT MMG (not LMG) and the carbine.


    TFB: The 6.5mm CT according to LSAT’s slides weighs 15.4 grams per shot, compared to the 12 grams per shot of brass-cased 5.56mm. In a couple of articles I wrote, I examined the weight penalty of using a round this heavy as a replacement for both 5.56mm and 7.62mm. Does the CTSAS program consider this weight penalty acceptable, or not? If so, is the idea to reduce the number of rounds carried by the infantryman in exchange for greater effectiveness of the individual projectiles, or is the 15.4 grams just the current state of things, the weight of ammunition expected to decrease with development?

    KP: Since the 6.5mm is a heavier projectile than the 5.56mm, and it requires more propellant to achieve the necessary velocity, it will probably always be heavier than the 5.56mm round. This is an option that is being offered for a round that provides considerably more range and performance than even the 7.62mm, so that is actually a better comparison. The trade-off between weight and performance is totally up to the user community, and not the technology developer.


    TFB: Textron recently showed off their mockup for a 6.5mm CT carbine at AUSA. According to their representatives, the 6.5mm CT round they are using (I am assuming this is the same round as the CTSAS cartridge?) produces 3,000 ft/s muzzle velocity from the carbine’s barrel with a 123gr bullet, for almost 3,400 Joules. This is much closer to 7.62mm NATO performance than 5.56mm. How does this change in performance affect the rifle, and is this performance something demanded by Fort Benning requirements, something done deliberately by the CTSAS team, or a byproduct of the chamber volume of the 6.5mm round (which shares external dimensions with 7.62mm CT, correct?)?

    KP: This improvement in performance is being done deliberately by the CTSAS/Textron team (we are all on the same team). The rifle is being developed concurrently with the ammunition, and so there are no expectations that it will degrade the performance of the weapon. The 6.5mm round performance actually exceeds the performance of the 7.62mm round, at a lower weight and impulse. The 6.5mm and 7.62mm CT projectiles are being packaged in the same cartridge case only for convenience at this time. It allows us to use either round in the weapons with only minimal changes to the weapons (mainly the barrel). The 6.5mm cartridge could be made slightly smaller in the future.


    The Textron 6.5mm CT Carbine. Taken from a slide in the 2016 NDIA Armaments Conference CTSAS presentation given by Kori Phillips.


    TFB:Is there a worry that the vastly increased performance of the new round will adversely affect shooter recovery time and weapon handling in fully automatic mode?

    KP: No, shooter controllability has been accounted for in the weapon and ammunition design.


    TFB: How was the 6.5mm caliber chosen as the third CT round? What requirements were involved that led to the selection of that configuration? What thresholds needed to be met, if any, for the 1,200m range requirement (e.g., “retained energy of 300 ft-lbs at 1,200m”)?

    KP: The NDIA briefing that I gave at the Armaments System Forum in April 2016 describes the caliber optimization study in some detail. The basic concept was to provide required velocity at a specified range (not shown) and threshold impact energy at 1,200 meters, at the lowest possible impulse and weight.


    TFB: The .264 USA is often mentioned alongside the 6.5mm CT as a sort of “conventional counterpart”. The .264 USA is however considerably less powerful (~2,700 J vs. ~3,400 J). The AMU obviously being a separate entity to Picatinny, has there been any cross-pollination there?

    KP: The AMU did provide us feedback on the actual projectile, which is very similar for both systems. I am not aware of the characteristics of their cartridge, but they are constrained somewhat by the use of a legacy cartridge and weapon design, and the goals of their program are slightly different.


    TFB: The weight savings of a 5.56mm CT round is considerable versus the standard brass-cased variety. Does the CTSAS program see a future for 5.56mm CT or not, and in either case why?

    KP: It depends whether the user community prioritizes weight or performance.


    Original caption: “Spc. Luke Anderson fires the LSAT LMG at a 100-meter target at Fort Benning, Ga.” Image credit: Eric Kowal, RDECOM. Public domain.


    TFB: The current Textron 6.5mm CT carbine uses magazines of 20 rounds capacity, 33% less than that used by the current M4 Carbine. Is this deemed an acceptable decrease, and if so why? If not, are higher capacity magazines being sought/developed?

    KP: We could not find any doctrinal guidance on how many rounds should be in a magazine for a combat rifle, and when we looked at 7.62mm rifles for comparison (like M14 and MK17), they have 20 round magazines. The only impact of having a higher capacity magazine would be the overall size (and weight) of the magazine, since these rounds are bigger than 5.56mm rounds.


    TFB: Right now, the weight of equipment carried by the infantryman is very high, which presumably means there is a crunch on how much weight can be added or needs to be saved for various pieces of equipment. The LSAT/CTSAS team has already innovated in this area, but the Textron 6.5mm CT Carbine is still heavier (with heavier ammunition) than the existing M4/M4A1. Moving forward, how does CTSAS plan to reduce the weight carried by the soldier, and will we see a further weight decrease thanks to the technology being developed through this program?

    KP: The 6.5mm system may increase weight slightly over the M4 if it is carried with the same number of rounds of ammunition, but if the ammunition proves to be more capable, some decisions could be made to change the standard combat load from 210 rounds (current) to something less (notionally enough to balance the weight between the two systems). The CTSAS/Textron team is not in a position to make these kinds of decisions, but we wanted to offer the decision makers an option that would provide a capability that exceeds what they currently have at the smallest possible weight penalty. There is always opportunity for additional weight savings or tradeoffs, depending on the priorities of the users.


    TFB: I mean, that 6.5mm CT round is a monster! It’s producing like double the energy of an M4. Is that something you were able to get away with because you’re getting better efficiency out of the propellant, and also because you have the soft-recoil LMG?

    KP: The thing we were using for comparison was weapon impulse, so we didn’t consider the weapon platform. We wanted it below a certain threshold, but because the 6.5 was a fairly small bullet, we could jack up the velocity and still not go above our impulse threshold. We ended up using the 123gr Sierra MatchKing for testing.


    TFB: The 1,200 meter distance mentioned in your presentation didn’t end up being what I thought it was. How did you come to that?

    KP: That is just a standard test distance, there’s no operational requirement associated with it. When they test 7.62mm guns, they test them out to 1,200 meters. We chose that number because that was a good place to compare what our bullet would do to what 7.62mm would do. It’s more of a medium machine gun range, and we wanted to push the MMG out beyond what an LMG would do.


    TFB: That sort of suggests that the 6.5mm CT is intended to be kind of a maximum configuration round.

    KP: In addition to the carbine, the 6.5mm ammunition will be used for the CT Medium Machine Gun , which could replace the M240B and M240L. We wanted to make sure it could do as well as that weapon system or better. The CT Medium Machine gun with 800 rounds of CT ammunition (either 6.5mm or 7.62mm) weighs the same as the current M249 with 800 rounds of brass cased 5.56mm ammunition, and provides far more capability. And when it’s done, the carbine will weigh around 8 pounds, which is more than an M4, but keep in mind the performance exceeds a 7.62mm rifle, which tend to weigh significantly more.

    Nathaniel F

    Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. He can be reached via email at [email protected]