The Farquhar-Hill self-loading (semi-automatic) rifle was a joint development of two British gentlemen, Moubray G. Farquhar and Arthur H. Hill. Their original invention, patented in UK in 1908 and in USA in 1909, was a long-recoil operated rifle with rotary bolt locking. The key feature of this firearm was the fact that recoil energy of the moving barrel was stored in the intermediate spring. Upon discharge, barrel recoiled back and forth while still locked with the bolt, compressing the intermediate spring on recoil. Upon return of the barrel into the forward position the energy, stored in the intermediate 'action' spring, was used to cycle the bolt back and forth, extracting and ejecting the spent case and feeding a fresh round into the now stationary barrel. The main goal was to achieve smooth and reliable cycling of the bolt, but the design was very complicated and thus badly suited for a military firearm. By 1911, Farquhar and Hill revised their rifle, changing its source of energy from barrel recoil to more convenient gas operated action. This new weapon also utilized intermediate spring as a source of energy for cycling of the bolt, but the barrel was now stationary, simplifying design and making it potentially more accurate and reliable. During following years this design was further refined and tested by British Army on several occasions. This rifle was initially chambered for the new ".303 rimless" round, designed by necking up the 7.65x53mm Belgian Mauser case and loading it with British-issue Mk.VII bullet of .303 caliber. Later on this experimental loading was discarded in favor of the standard issue .303 British ammunition. After several trials, including troop trials at the front, in 1918 the Farquhar-Hill rifle was found to be suitable for military use, and an official request was issued for procurement of as much as 100,000 of Farquhar-Hill rifles for British forces fighting on the Continent against Germany. Official nomenclature assigned to the military Farquhar-Hill rifle in August 1918 was "Rifle. .303 inch, Pattern 1918". However, hostilities of the Great War ended before production facilities were allocated for this rifle, and in the view of an upcoming peace the requirement for manufacture of Farquhar-Hill rifles was dropped in 1919. During 1920s and early 1930s Farquhar redesigned this rifle into a light machine gun of lightweight design, fed from top-mounted pan magazines. This machine gun, known as the Beardmore-Farquhar, was also tested by British army on several occasions but was ultimately rejected for variety of reasons.
The Farquhar-Hill self-loading (semi-automatic) rifle, as it was formally accepted by British army in 1917, was a gas-operated weapon. It had a long stroke gas piston, located below the barrel and fitted with two springs – one more powerful and one less powerful. Upon discharge, gas piston was pushed rearwards against both springs, compressing them, while bolt group remained stationary. The more powerful spring (action spring) had latches on both ends, and during the early stages of discharge its rear end was held by rear latch while its forward end was compressed by the gas piston. At the end of the gas piston rearward stroke the front of the powerful action spring was captured by its front latch, while being disconnected from the gas piston; at the same time its rear latch was released to allow compressed spring extend rearwards, against the operating rod connected to the bolt carrier, and release its energy to cycle the bolt group. At the same time, gas piston was forced forward by its own return spring, which was relatively weak. Upon opening of the breech, the front latch of the action spring was automatically released, and the uncompressed action spring returned into its forward position, ready for the next cycle. The bolt group was returned into the battery by its own return spring, which also was noticeably less powerful than the action spring. All this complication was invented to ensure smooth cycling of the bolt group regardless of the variations in the ammunition, and somehow decrease felt recoil. The barrel locking was achieved by a fairy conventional rotary bolt with dual locking lugs at the front. Feed was from detachable drum magazines with 19-round capacity. Rifle was fitted with wooden stock with semi-pistol grip. Complicated gas and spring action, which was located below the barrel, was enclosed in the sheet steel forend. To ensure comfortable handling, rifle was fitted with vertical foregrip under the forend, whose position could be adjusted along the specially fitted rail with several mounting holes. The Farquhar-Hill self-loading (semi-automatic) rifle was provided with adjustable iron sights and sling swivels. Provisions were made for mounting of a knife-type bayonet, located below the forward part of the barrel.