The Department of Defense has requested $111.2 million USD from Congress to develop their next-generation squad weapon by 2023. The request includes funding to procure prototypes for a next-generation weapons system, as well as funding for new 6.8mm ammunition for this weapon. This is intended to replace the traditionally used 5.56mm ammunition. Interestingly, the ammunition has been chosen, but the carbine itself has yet to be decided upon. Several models are being designed to fit this new caliber. While it has not been outright stated, Special Forces operators are almost certainly testing these new prototypes.
A Texas-based ammunition company designed this new cartridge in an effort to provide soldiers with "significant logistical and operational advantages over traditional brass-cased ammunition, including substantially increased effective range and muzzle energy, drastic reduction in cartridge weight and enhanced capacity."
This cartridge features a polymer casing, which is claimed to be approximately 30% lighter than brass casing. In practical terms, this has huge implications for Operators as the total ammunition they can carry will be increased. However, it is still subject to the issues that have traditionally occurred with polymer casings.
This cartridge is advertised as having a reduced heat transfer, which is technically true, but not without its own set of issues. The short-term heat-transfer will be less to the chamber area because the polymer will not transfer heat to the chamber area. In theory, this sounds good, but causes problems in practice. Energy cannot be created or destroyed, only directed.
In this case, the energy will be directed straight forward. So the long-term heat transfer to the chamber and barrel will still happen, just in a different way. Rather than the case absorbing some of the thermal energy, and then removing it from the system upon extraction, the energy will instead become focused on the case mouth. The heat will then hit the throat of the barrel, and be conducted back into the chamber area, otherwise known as differential heating. By heating the internal elements at different rates, the metal undergoes accelerated erosion and increases the potential for cracking. Brass-casings absorb and remove thermal energy from the firing block, resulting in a much more even heat distribution in the chamber. Furthermore, it is easier on the barrel because it isn't projecting the same heat down the throat. With a polymer casing, the barrel will probably suffer throat erosion. Essentially, the normal heat distribution will be moved forward into the barrel, eroding and damaging it faster than what would happen with brass-cased ammunition.
While the potential weight differential in the ammunition would make a huge difference, the proposed weapons system may suffer the same fate of other prototypes that looked to replace the M16-style weaponry. It will need to be affordable for the military to purchase, but it cannot be made with cheap materials due to the use of polymer casings. The differential heating caused by these cartridges will destroy poorly or cheaply made weapons. Traditionally, the Army has targeted (no pun intended) weapons that were easy to maintain, and produce, and cheap to shoot. Therefore, the differential heating will almost certainly need to be addressed in the design of the weapon itself, potentially creating complexity that wasn't necessary before. Greater complexity creates more opportunities for malfunction. If the new rifle does not address the differential heating, and do it at cost, then it will likely be marked down in the books as yet another weapon that could not beat the AR-type design.
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