The RAI Model 300 and Model 500 rifles were designed specifically by engineer Jerry Haskins for military service with special elements of the United States Army during the early part of the 1980s. The rifle was developed around a lightweight body that was made relatively easy to convert to 7.62x51mm NATO and 12.7x99mm NATO cartridge chamberings, the latter centering on anti-material battlefield duties. The result of this work became the Model 300 and Model 500, respectively, which were both evaluated by Army special forces. In the end, only the .50 caliber (12.7mm) version - the Model 500 - was taken into service and this only in limited number.
The arrival of the RAI rifle, also known as the "Haskins Rifle" after its designer, came at a time when the .50 caliber anti-material rifle was not yet en vogue. The first such weapons were debuted by the Germans in World War 1 (1914-1918) through the "T-Gewehr" rifle (detailed elsewhere on this site) intended to tackle the threat of the new British tanks. This rifle fired a near-standard infantry rifle cartridge but held enough power to pierce the protection offered by these clumsy machines. Truer anti-tank rifle weapons were later seen during the fighting of World War 2 where several of the major powers fielded some form of the type - the British with their Boys .55, the Soviets with a Simonov and Degtyarev mark and the Japanese with their Type 97. Finland, Poland and Germany also contributed to this unique category with local types all their own.
The anti-tank rifle was eventually found to be doubly useful in the "anti-material" role and, in the 1970s, there proved renewed interest in such an infantry-level system. Development eventually led to the excellent Barrett M82 for the American military while the Harris / McMillan brands also contributed other examples. Other nations eventually jumped into the ring with their own designs including Hungary with their "Gepard" line and the small arms branch of Denel for South Africa (NTW-20). Today the anti-material rifle is a fixture of most any respectable army service with the most popular being the Barrett models.
The operation of the RAI Model 500 gun was of manual bolt-action and feeding of the cartridges was by way of a five-round detachable box magazine inserted into a well in the usual way (ahead of the trigger group). The shoulder stock was collapsible for compactness and arranged as "skeletal" for a weight-savings measure. The stock was customizable to an extent by the shooter and included a cheek rest. The barrel was free-floating, the assembly not touching the forend of the stock at any point, and constructed to a heavy precision-based tolerance for absolute accuracy at range. A telescopic scope (removable) was fitted over the receiver for ranged firing. A folding bipod was affixed to a short forend section located under the barrel assembly to aid in prone-based firing. Beyond customization of the shoulder stock component, the trigger was also fully-adjustable to suit the firer's pull requirements. The lightweight nature of the gun's construction, and the ability for it to be broken down quickly, aided in the weapon's travel profile considerably.
Overall weight of the system (sans its scope) was 5.7 kilograms and the barrel assembly measured 610mm in length. Muzzle velocity of the outgoing bullet reached 800 meters-per-second and effective range was out to 1,300-2,000 meters. A trained shooter could expect to land the round within a space of a "small" window or box at even extreme ranges, such was the accuracy of this weapon.
The RAI rifle was also used to trial the experimental 8.58x71mm cartridge which, later, became the popular .338 Lapua Magnum round in widespread circulation today.