The CRAZY Guns Of The US Army's SPIW Program

From Project SALVO to the SPIW Concept

The discussion opens with the US Army’s search for more effective small arms after World War II. Studies showed that most combat injuries occurred at shorter ranges than expected, and that sheer volume of fire mattered more than extreme rifle accuracy. A 1 MOA rifle and a 4 MOA rifle had similar hit probabilities at typical engagement distances. In 1951, Project SALVO explored ways to increase firepower per soldier, testing duplex and triplex cartridges as well as flechettes, which are small steel darts. SALVO ultimately recommended duplex ammunition with two projectiles in a single case. However, the later Special Purpose Individual Weapon (SPIW) program in the 1960s focused on the flechette approach instead, inviting Harrington & Richardson, Winchester, AAI, and the government‑run Springfield Armory to develop experimental individual weapons around high‑velocity flechette projectiles.

Harrington & Richardson’s Multi‑Bore Flechette Rifle

Harrington & Richardson submitted one of the strangest SPIW prototypes, a multi‑bore rifle firing a triple flechette cartridge. Each plastic‑cased round was triangular in cross‑section and contained three flechettes. The design used an open‑chamber revolving cylinder that fed belted ammunition sideways through the action. As the belt advanced, an open chamber picked up a round, rotated it into line with the three bores, fired all three flechettes simultaneously, then rotated further so the spent case could fall out while still attached to the belt. Because the chamber was not fully enclosed, the case had to contain most of the firing pressure on its own. Uneven muzzle pressure could slow or stop some flechettes, risking bore obstructions and erratic flight. The rifle weighed around 24 pounds, was mechanically complex, and only held 20 cartridges to meet the 60‑flechette requirement. The Army deemed it unsafe and refused to live‑fire test it.

SPIW Requirements and Design Constraints

The SPIW program imposed demanding requirements that heavily influenced every prototype. Each weapon had to provide 60 rounds of point ammunition, whether bullets or flechettes, and offer semi‑automatic, burst, and full‑auto modes. Designs also had to accept a three‑round grenade launcher, a bipod, and a bayonet. The concept behind flechette ammunition was a very light, high‑velocity projectile that produced low recoil and allowed a relatively lightweight rifle with a high cyclic rate. However, bolting a three‑round grenade launcher to the front of such a light platform shifted the balance forward and undermined handling. The added mass conflicted with the original goal of a nimble, low‑recoil individual weapon. These conflicting requirements contributed to awkward weight distribution and complicated engineering choices across the SPIW submissions.

Winchester’s Hybrid Open‑ and Closed‑Bolt SPIW

Winchester’s SPIW entry, which did not advance to the second round of trials, incorporated several unusual operating features. It used a hybrid firing system: in semi‑automatic mode it operated as a closed‑bolt rifle, while in burst and full‑auto it switched to open‑bolt operation. In automatic fire, the bolt stayed to the rear until the trigger was pulled, then drove forward, chambered a round, and fired immediately. The weapon fed from a 60‑round drum magazine to satisfy the SPIW ammunition requirement. Winchester used a short‑stroke gas system, described as a gas tappet, and combined it with a soft‑recoiling arrangement where the barrel reciprocated slightly during cycling. The barrel initially moved rearward with the bolt, then the bolt continued into a special housing and traveled further on its own. This staged movement was intended to manage high flechette pressures and potentially soften recoil, but reports indicated it did not significantly improve recoil characteristics.

Winchester’s Blow‑Forward Three‑Round Grenade Launcher

One of the most mechanically interesting elements of Winchester’s SPIW package was its under‑barrel grenade launcher. It used a blow‑forward operating principle, where firing a grenade round pulled the barrel forward through friction as part of the cycle. The launcher held three grenades: one aligned at the rear feed position and one in each of two side compartments. After the first round fired, the forward movement of the barrel opened an ejection port on the bottom, allowing only the shorter fired case to drop free. As the barrel reached the end of its forward travel, it tripped a mechanism that fed a fresh grenade from one of the side compartments into position. The unfired cartridge was too long to fall through the ejection port, so it remained in place until the barrel, driven by spring pressure, moved back and effectively closed around it to complete chambering. Despite its clever sequencing, this launcher was not judged successful, and Winchester’s overall SPIW system was dropped from further development.

Transition to Springfield Armory’s Government Submission

After covering Harrington & Richardson and Winchester, the discussion turns toward the government’s own SPIW entry from Springfield Armory. At the time, Springfield was a federal armory rather than a private company, and its approach differed enough that it almost amounted to multiple distinct submissions under one umbrella. The narrative sets up Springfield’s work as a contrast to the earlier, more obviously problematic designs, suggesting a more modular concept for the Special Purpose Individual Weapon. Details of Springfield’s specific configurations and performance are introduced after this point, continuing the examination of how the Army and its contractors tried to reconcile lightweight flechette rifles with integrated grenade launchers, high ammunition capacity, and multi‑mode fire control within a single individual weapon system.