Mehmed IIA and Günther SchlonkB*
Specific: We applied the principals of green chemistry and OH&S to light artillery, and herein we report our findings.
Abstract: The difference between a mortar and a pipe bomb turns out to be a lot less than you’d think
Introduction Historically, mortars have existed as a means of delivering explosives to people you don’t like, when they are located between about 200 and 5000 meters from you. They occupy the space between the personal touch of a hand grenade and the faceless hostility of conventional artillery, with the benefit of being quite portable. Modern mortars typically consist of a base plate supporting a metal tube, which can be accurately angled and elevated in accordance with how far the physics department is from your firing position (Figure 1A). The rounds fired by these mortars resemble finned metal sperms, with a payload in the head, and a propellant charge in or around the tail. When a round is dropped down the barrel, contact with the base initiates the firing pin, which ignites the propellant charges and launches the round from the barrel like yesterday’s Taco Bell.
While the stolidity of this design has allowed it to persist unchanged for over a century, you can’t get tenure by writing papers about how everything is fine, and the hairline fracture we’ve spotted is the nature of the propellant. This is typically a nitrocellulose-based composition. While these materials are safer than a paraben milkshake, misfires can occur. Premature ignition of the propellant can result in a spontaneous dactylectomy for the operator, or in the mortar itself being launched in several directions at once. In this paper, we disclose a potential remedy to these ills by devising a safer, greener mortar propellant.
Methods and Results Nitrocellulose is like our uncle Jim after a bottle of Jack: it already contains all the required ingredients for its own destruction. That’s what makes it dangerous. To make a safer mortar propellant, we took the obvious step of finding two components that were inert by themselves, but explosive when combined. Naturally, we settled on sodium metal and water. Water is ubiquitous,1 innocuous2 and cheap.3 Sodium is lightweight, healthy,4 and stable in isolation. However, a vigorous and potentially explosive reaction results when they are combined, particularly in an enclosed space. This is the result of combusting hydrogen gas, as well as a coulomb explosion.5 As no carbon or nitrogen oxides are produced in this reaction, it is more environmentally friendly than nitrocellulose.
When designing our sodium-mortar, we kept considerations of cost and sustainability foremost in our minds. This is because our research group is fucking skint. As such, while we retained the metal barrel from conventional mortars, we decided to replace the base plate, bipod and recoil systems with a stick (Figure 1B). One end of the stick is attached to the firing tube with the aid of a hose clamp, and the other end is rammed into the ground at the desired elevation. The base of the firing tube is loaded with a protic solvent such as water, and a projectile capped with sodium is fitted to the end of the barrel and held in place with a firing pin. When a string attached to the pin is pulled, the pin is withdrawn, dropping the projectile down the barrel. As the sodium is forced into the water by the projectile’s momentum, a vigorous reaction then propels the round skywards, hopefully at speeds approaching Mach fuck. We were confident in the strength of our design, but we decided to begin with a small-scale model nonetheless, as recommended by the International Committee for Improvised Explosive Experimentation.6 To that end, we used a piece of 0.5 inch PVC pipe as a barrel, and a sharpened stick (Eucalyptus globulus) as a base plate. The projectile consisted of a 12 g ball-bearing to simulate the payload, and a 1 cm hex nut packed with sodium (300 mg) as the propellant module. These two components were then encased in a 0.7 mm layer of electrical tape, which was expected to function as a makeshift discarding-sabot (Figure 2).
With the apparatus thus assembled, it was transported to the West Failian Ballistics Testing Range and deployed with a barrel elevation of 45°. The barrel was charged with 10 mL of deionised water, the projectile was loaded, and the firing pin was removed. There was an audible plop as the projectile reached the water, followed by the evolution of smoke from the barrel (Figure 3A). At t = +7 s, the mortar discharged with a sharp report, and the projectile left the barrel at an estimated speed of 120 feet-per-minute. The ballistic arc reached its peak at ca. two barrel-lengths from the ground, and the fall of shot was measured at a range of 55 cm. At t = + 8 s, residual hydrogen escaped and ignited the PCV of the barrel, liberating chlorine gas and copious smoke (Figure 3D, 3E).
This test clearly demonstrated the viability of our mortar design. A small mass of sodium proved capable of launching a much heavier projectile in a high ballistic arc, using only water as co-propellant.
That being said, this initial design clearly exhibits several deficiencies, most prominently in that it was significantly underpowered. Modern weapons must be accurate over ranges significantly longer than the length of their own barrels, and our “Water Mortar Mk. 1” was could be outranged by a battering ram. Figure 3C clearly shows a large amount of propellant gas escaping around the sides of the projectile, and this windage is at least partially responsible for the disappointing performance. Furthermore, the ignition of the mortar’s barrel clearly demonstrated the unsuitability of PVC as a construction material. With these notes in mind, we set out to improve our device on a larger scale. The “Water Mortar Mk. 2” featured several major modifications. The PVC barrel was replaced with a 40 cm length of 7.62 cm galvanised steel pipe, making the resultant weapon a 3-inch 5-calibre smoothbore howitzer. The stick was replaced with a sturdier branch of Eglobulus, and attached to the barrel via sledgehammer. A lighter projectile was also desired, and a prototype was fabricated from PVC, with a payload chamber in the head and an open, cup-shaped propellant chamber in the base. Twelve steel washers (45 g total) were used to simulate the warhead, and 10 g of sodium metal propellant was loaded into the fuel chamber (Figure 4). Finally, the aqueous co-propellant in the mortar tube was replaced with 80 mL of concentrated sulfuric acid, for increased power.
The Water-Mortar Mk. 2 was set up to test fire as before, and the firing pin was withdrawn. However, at t = +35 s, no reaction was observed. A technician was persuaded to approach the weapon, and reported hearing “an ominous gurgling, as if Mr Creosote had just slammed a plate of pork sashimi and a triple espresso”. Despite this promising sign, the weapon had still failed to discharge, even at t = +60 s. Following some further coaxing and threats of physical violence, the technician was instructed to tap the weapon with a “firing stick”. At the third tap of the stick, the mortar discharged (Figure 5).
Unlike the small-scale test, the Mk. 2 fired with extreme violence. A giant flaming phallus erupted from the barrel with Oppenheimeric audacity, followed by a shower of burning sodium sparks and billowing clouds of Na2SO4 and H2SO4. The ignition of the propellant was accompanied by a deep-throated thumping boom one could hear not just with the ears, but also with the kidneys. Due to the nature of the explosion, the projectile could not be located in the slow-motion footage, but a technician reported observing a burning mass of PVC and duct-tape arcing over the tree line at the far end of the firing range. This would correspond to a range of at least 60 metres. Unfortunately, the ensuing bushfire made the recording of accurate data challenging, as all remnants of the projectile seem to have melted in the inferno.
Discussion and Conclusion
We have demonstrated that a mortar employing sodium metal and sulfuric acid as propellants is technically feasible. We have also demonstrated that building one of these things is a terrible idea. Given the nature of its combustion products, the 3” Water-Mortar is closer to a chemical weapon than a piece of artillery. It could perhaps be deployed to generate smokescreens, or flush insurgents out of cover, but its most practical applications likely lie in the realm of psychological warfare, because if one’s enemy is brave enough to use this thing, they’re clearly out of their fucking minds.
Acknowledgements
G.S. offers his most sincere apologies to the technical staff of the West Failian Ballistics Testing Range. For everything. Really.
Notes and references
1. Note: Except for a lot of the places where recent wars have been fought.
2. Note: Except when it contains sharks.
3. Note: Except when flying with Ryanair.
4. “Biscuits that Burst in the Mouth: Chocolate- and Sodium-Chip Cookies” A. Danger, Davo, G. Schlonk, 2023, J. Immat. Sci., 3, 36–39.
DOI: https://jabde.com/wp-content/uploads/2022/11/Exploding-Cookies-1.pdf
5. “Coulomb explosion during the early stages of the reaction of alkali metals with water.” P. Mason, F. Uhlig, V. Vaněk, et al. 2015, Nature Chem., 7, 250–254. DOI: https://doi.org/10.1038/nchem.2161
6. ICIEE Handbook, 1990.