Future Firearms Ammunition Technology 008: Plastic-Cased, Telescoped Ammunition - Lightening the Load, Pt. 4
Previously, we discussed different concepts for lightening the soldier’s load, including aluminum-, composite-cased and caseless ammunition. Today we’re going to look at the weight-reducing concept that many believe is the horse to bet on when it comes to next-generation small arms ammunition, and that is the plastic-cased telescoped ammunition concept, often referred to as cased, telescoped ammunition (CTA).
Where plastic-cased composite ammunition addresses the problem of extracting a polymer cartridge case by incorporating a metallic rim or base, the CTA concept takes a page from the playbook of caseless ammunition and asks the question: Do we really need to be pulling cartridges out of the chamber? Instead, CTA weapons are designed to push spent casings out of the front or side of the chamber, using the incoming round as both extractor and ejector. This layout requires a straight cartridge of constant cross-section, which engineers have often coupled to a telescoped layout where the projectile is buried in the round’s propellant.
This concept does eliminate the problem of rim tearing with polymer ammunition, but it presents other problems. To facilitate this kind of cycle, a CTA weapon needs to have a separate chamber that moves so that the front end of the chamber is opened for ejection, but this also means that, like a revolver, the gap between the chamber and the barrel is not sealed. CTA weapons can address this in a few ways, including fixed, expandable chamber sealing devices attached to the chamber or barrel, or by using a sliding lockless design, but the problem of high pressure gas leakage remains a big challenge for CTA weapons engineers. Further, telescoping ammunition has some serious problems with gas leakage in front of the bullet, since it is difficult to keep the propellant from out-racing the projectile and burning ahead of it. In the most recent CTA ammunition configuration, this problem has been circumvented simply by not fully telescoping the round, and keeping the propellant behind the ogive of the projectile.
However, where the concept holds the most promise is in weight reduction: the CTA ammunition developed for the US Army’s Lightweight Small Arms Technologies program have demonstrated weight reductions of 32-36%, a massive improvement versus the old brass cased paradigm. Also, since the projectile and primer are the only metallic components in CTA ammunition, a great deal of strategic material could be saved as well if CTA ammunition proves feasible.
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 nathaniel.f@staff.thefirearmblog.com.
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When i was at Rodman Lab in the 70's the military had been trying to come out with these . Hughes Gun System was working on it.
Why can't the base be a veneer of primer, the next 80% be propellant, and the last 20% be a saboted round? Constant diameter, chamber:barrel, high sabot base surface area to bullet weight ratio to increase muzzle velocity, tiny waste if the sabot is plastic or low cost. The primer doesn't HAVE to be ignited by impact; it could be electrically ignited - or by impact/piezo spark. If weatherproofing is an issue, a light saran-like coating encapsulating the primer and propellant could still be breached by a strong-enough piezo igniter. For that matter, if the piezo or other-source electrical charge was carried by a conventional firing pin, it could break through the saran to deliver the ignition shock. The next round's sabot leading edge would clear the chamber of residue when loaded.
I'm sort of a sabot bigot, but apart from the challenge of selecting a sabot material that isn't of low dimensional integrity, so that the bullet is chamber- and barrel-concentric, I would think this would be eminently retrofittable (not a word . . .) to existing weapons with a (periodically) replaceable chamber insert. The other issue is that it's not just about weight; it's also about volume. Such telescoped or partially-telescoped rounds wouldn't take up as much room, so a given ammo pouch or container could carry a larger payload, you'd need fewer trucks for resupply, etc. Just a wild-eyed blue sky idea, but hey, even a blind squirrel finds a nut once in a while; who knows? Nice article.