A spotting rifle or ranging gun is a small-calibre rifle used as a sighting device for artillery. The ballistics of the spotting rifle are matched to those of the artillery piece, so that if a shot from the spotting rifle lands on the target, it may be assumed that the main weapon will also do so.
US Marines with a 106 mm M40 recoilless rifle, during the Battle of Huế
Chieftain, with the ranging gun barrel just visible above the main gun in the mantlet
The M40 recoilless rifle is a portable, crew-served 105 mm recoilless rifle made in the United States. Intended primarily as an anti-tank weapon, it could also be employed in an antipersonnel role with the use of an antipersonnel-tracer flechette round. The bore was commonly described as being 106 mm caliber but is in fact 105 mm; the 106 mm designation was intended to prevent confusion with incompatible 105 mm ammunition from the failed M27. The air-cooled, breech-loaded, single-shot rifle fired fixed ammunition and was used primarily from a wheeled ground mount. It was designed for direct firing only, and sighting equipment for this purpose was furnished with each weapon, including an affixed spotting rifle.
A deactivated M40 on display at the Philippine Army Museum
Ontos M50A1 with six 105 mm M40 recoilless rifles
Jonga, mounted with 105 mm RCL gun which destroyed most of the tanks during the 1965 and 1971 Indo-Pakistani wars
Greek Mercedes 240G M40 carrier. Note the metal guard to protect the engine from the gun blast.