While the MkII (1905) iteration of the Ross rifle had resolved most of the major mechanical problems form the MkI, it retained a number of characteristics that the Canadian (and British) military was not fond of. In particular, it was not suited to the use of stripper clips. Starting with experimentation on sporting rifles, Ross substantially redesigned the action for the final 1910 pattern – aka the MkIII.
The MkIII used a rotating bolt as before, but with six locking lugs in two rows of three, instead of two large lugs as the MkI and II. The magazine was replaced by a conventional single-stack design, with a stripper clip guide built into the receiver, and with a nicely adjustable rear aperture sight. This would be the model to equip the Canadian infantry who went to Europe to fight in 1914 and 1915 – and it is there that a new set of problems would begin to plague the Ross.
In keeping with its sporting legacy and reputation for outstanding accuracy, the MkIII Ross was made with a rather tight chamber, optimized for the excellent-quality Canadian production .303 ammunition. Britain had been forced to massively increase ammunition supply as the war lengthened, and British standards had widened to accept ammunition that was really of rather questionable quality. The SMLE rifles used by British forces had chambers made to accommodate this, but the Rosses did not. Canadian ammunition was supposed to follow the Canadian troops, but it was usually diverted to other services because of its high quality, and the Canadians left with ammo that was difficult to chamber or extract in the Ross.
This led to men having to beat open rifle bolts, which led to damage to locking lugs, in a viscous circle of escalating problems. By the time of the German gas attack at Ypres, Canadians were ditching their Rosses for Lee Infields by the thousands, despite specific orders to the contrary. General Haig finally had enough of the issues, and ordered the Ross removed from combat in 1916, to be replaced by the SMLE (which was finally available in sufficient numbers to arm the Canadian troops).