Short, Magazine Lee-Enfield sniper rifle with Periscopic Prism Company telescope (PPCo) sight - Arms of the First World War - Royal Armouries collections
My 1903 Sniper collection | Sniper's Hide Forum
First World War sniper rifle | NZHistory, New Zealand history online
Sniping From Below: Periscope Rifles in World War I - World War I Centennial