The Robinson S.R. Model 9 Machine Rifle, more commonly known as the Robinson SR-9, was an Anglo-Australian burst-firing constant recoil anti-materiel rifle designed by Russel Robinson and produced in prototype form only.
The SR-9 was designed from 1942 to 1943 by Russ Robinson, an Australian designer who was known for his work with constant recoil arms; the original plans were drawn up by Robinson on advice of the Ordnance Branch, USHQ Sydney. He drew up the plans alongside another of his projects, the S.R. Model 11.
Originally, the SR-9 did not receive any official factory backing, but eventually the weapon was considered for adoption due to the release of the All Arms Ack-Ack (A.A.A.A.) requirement in an attempt to protect truck convoys. For this, Robinson proposed two contenders for the requirement; one was the SR-9 and the other an inexpensive ball-ring mount based on two spun metal rings which could support any machine gun from .303 British to .50 BMG. This mount would be adopted as the A.A.A.A. mount and development of the SR-9 ceased.
The SR-9 was a burst-firing recoil-operated .50 caliber anti-materiel rifle meant to be fired from over the shoulder. The weapon feeds from a 16-round magazine inserted through the top of the weapon. Inside the weapon was also a chain which aided in the operation of the weapon.
As the weapon fires, the barrel recoils rearwards; the recoiling action drove a chain-operated bolt carrier locked to the barrel extension as the barrel slammed forward. Escapements located at each end of the chain allowed the barrel to be stopped by front and rear buffers in the event of misfire or hang fire.
A spur is located on the front pistol grip to allow it to be anchored to a surface such as a window. The weapon originally did not have a quick change barrel, but with the introduction of the A.A.A.A. requirement, one was added to the rifle. The SR-9 was intended to be fired in bursts as opposed to semi-automatically. The weapon was coated in some sort of matte black paint.