Spotting rifle (English Wikipedia)

Royal Armoured Corp Training (1980). "3: .50 in – Ranging Gun" (PDF). Pamphlet No. 33: Chieftain. Vol. 3: Armament. Ministry of Defence. pp. 41–54. Army Code No. 71274. Archived from the original (PDF) on 2013-12-27.
Royal Armoured Corp Training (1980). "16: .50 in – Ranging Gun" (PDF). Pamphlet No. 33: Chieftain. Vol. 3: Armament. Ministry of Defence. pp. 311–314. Army Code No. 71274. Archived from the original (PDF) on 2013-12-27.

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Royal Armoured Corp Training (1980). "3: .50 in – Ranging Gun" (PDF). Pamphlet No. 33: Chieftain. Vol. 3: Armament. Ministry of Defence. pp. 41–54. Army Code No. 71274. Archived from the original (PDF) on 2013-12-27.
Royal Armoured Corp Training (1980). "16: .50 in – Ranging Gun" (PDF). Pamphlet No. 33: Chieftain. Vol. 3: Armament. Ministry of Defence. pp. 311–314. Army Code No. 71274. Archived from the original (PDF) on 2013-12-27.