The British Army Sniper Rifle from the 1930's until 1989.
After the adoption of the 7.62x51mm round as the NATO standard rifle round in 1950s, British Royal Small Arms Factory (RSAF) at Enfield Lock developed a conversion for many surplus .303 British calibre Lee-Enfield SMLE No.4 rifles. The conversion included new, heavy barrel, chambered for 7.62mm NATO ammunition, shortened forend and handguard. This conversion was intended for competitive shooting. The civilian version had been known as Enfield "Envoy" match rifle, military target rifle was designated as L39A1. Both versions featured adjustable open sights.
Later, with the addition of the scope mounting bracket to the left side of the receiver, the L39A1 became the L42A1 military sniper rifle. The effective range was considered to be 600m for this weapon, though, by the 1980's, that was debatable with some weapons as the deterioration of the reticles in many scopes meant that the sight post was covered in fur, making accurate placement of the shot at maximum effective range quite difficult.
The L42 was used in the Falklands war to great effect, with Argentinian Snipers being counter-sniped and killed.
One of the fun parts of using the L42 was the attempts to avoid something called 'Hawkins Eye'. This was a shooting position developed by a sniper of that name. The objective was to create as low a profile as possible to avoid detection, and to achieve this, the Hawkins Position was developed whereby the butt of the weapon was placed on the ground, with the firer at right angles to the weapon, supporting the front end by holding the fore-sling attachment with that arm locked to control the recoil. If the arm wasn't firmly locked, the recoil from firing would throw the weapon backwards with the rear of the scope (the occular bell) slamming into the eye socket of the firer. The result would be anything from a cut brow to a proper closed-eye shiner, with much resultant mocking from fellow snipers.
Early in the 1970, RSAF developed a police version of the L42A1, called "Enforcer". It differed from L42 by having more sporterised(wtf?) butt stock with semi-pistol grip and integral cheek piece. It also used match type open sights and commercial telescopic sights.
Production of the "Enforcer" and L42 rifles ceased circa 1985, and it was replaced in military service by Accuraly Intl. L96A1 rifle.