1. Lee-Enfield SMLE Mk III**: The British introduced the Lee-Enfield SMLE Mk III* rifle in 1907. It was chambered for the .303 British cartridge and saw extensive use during World War 1. Some of these rifles were equipped with a variety of optical sights, including the Pattern 1914 Telescope Sight and the Pattern 1918 Telescope Sight.
2. Mosin-Nagant M1891/30**: The Russian Imperial Army used the Mosin-Nagant M1891/30 rifle during World War 1. This rifle was chambered for the 7.62x54mmR cartridge and was known for its ruggedness and reliability. Some M1891/30 rifles were equipped with the PU (Pechenegskiy Universitet) scope, which was introduced in the early 1930s.
3. Mauser 98**: The German Mauser 98 rifle was used by German forces throughout World War 1. It was chambered for the 7.92x57mm Mauser cartridge and was a highly accurate and reliable weapon. Some Mauser 98 rifles were equipped with various telescopic sights, including the Zielfernrohr 1915 (ZF 15) scope and the Zielfernrohr 1918 (ZF 18) scope.
It's important to note that while these rifles were equipped with scopes, the use of optical sights was still relatively limited during World War 1. Most soldiers relied on iron sights for aiming and the concept of specialized sniper roles was still in its early stages.