TFB:

Previously, we discussed trying to lighten the soldier’s load by making the cartridge case out of different materials, including aluminum and compositing the case out of polymer and metal. Yet, wouldn’t the lightest possible case configuration be… Having no case at all? That’s the thinking behind one of the most ambitious ammunition configurations there is, the case-less round.

Of course, it’s true that before the metallic cartridge casewas invented, essentially all ammunition was caseless, but today the term “caseless” refers to ammunition that is self-contained, but with a body made of combustible propellant that directly contributes to sending the projectile out of the gun’s barrel. This concept is as elegant as it is simple; after all, making every part of the round work at killing the enemy can only be a good idea, right? Well, it’s not so simple as that, because economically producing caseless ammunition suitable for automatic weapons has proven to be an incredibly technically complex challenge. For starters, there’s a fundamental contradiction to the concept: Gunpropellants need to expose a certain amount of surface area to igniting flame in order to work properly and have the correct burn rate, but a caseless round needs its propellant to be consolidated into a single solid chunk which is durable enough for storage, shipping, and field use. This requires some kind of “disintegrator” charge – which may be provided by the primer – that breaks up the consolidated propellant during ignition, increasing its surface area. Also, caseless ammunition lacks any protective barrier between the propellant and the chamber, which may be very hot after a string of fire. This lack of a protective envelope reduces the threshold at which ammunition cooks off inside the weapon, a serious concern for a military small arm. Finally, caseless ammunition also cannot gain the benefit of disposable breech sealing that comes built-in to the modern metallic cartridge, so sealing must be accomplished some other way. All of these problems are difficult at low production levels, and impossible at the volumes required for a modern military round.

In fact, these challenges are so great that it’s unlikely that the concept will become feasible within the next few decades. However, if the considerable technical challenges are somehow surmounted, caseless ammunition offers the maximum reduction in ammunitionweight possible with conventional projectiles, while also facilitating extremely high rates of fire, due to the elimination of the extraction and ejection phases of the cycle.

From an engineering standpoint, it’s an awful idea.  Just terrible.  Even if something can be done – and I doubt this can ever be achieved – there is an engineer’s adage (I made it up and have used it extensively mentoring my young engineers) that comes to mind.

Margin is your friend.  Court her and be jealous for her.  Don’t cut corners, give yourself room to degrade, corrode, erode, design below your limits, and give yourself a margin of safety.  The larger the better.  Sure, too large won’t work because it is the enemy of functionality, creates physical interferences, causes components to be too heavy, and creates unnecessary expense.

But the other side is that lack of safety margin kills people.  It costs money, time, broken structures, systems and components, and it ruins companies.  My suggestion to the companies trying to do this is simple: this is a sweet, sweet siren song sung by an enchanting lass, but the cost of making all of that money and being famous may be your reputation, your company or even your life.

Ignore that song.  Get back to work designing better firearms and ammunition.  Forget caseless.