Ross Mark III (M1910) Rifles sent with the Canadian Expeditionary Force to Britain and the Front in France were reamed out to “LC” Chamber specifications…The Body diameters were increased, and the Shoulder moved Forwards somewhat, after Poorly-Manufactured British ammo caused a lot of Jams in the Flanders Mud n( Specifically from two or three “New Factories” (M, J, and N) because the shoulder Position was not correctly formed when, after filling the case with cordite, the neck and shoulder were formed around the Bullet.
The Ross Rifles were toleranced for Canadian Peace Time ammo, and with this worked Fine… in the trenches, Soldiers soon got to “Trying out” all their ammo before entering the Line, and Lots with H/S as marked above, were rejected and sent to MG units (the Heavy ramming force of the Vickers soon “full length sized” the Defective cases)
This QA problem ( the New Factories had NO experienced floor staff, only civilians off the street). The Technicians from Nobel and BSA could not cope with the Large volumes required in 1915 and early 1916, when Most of the defective shaped cartridges are found.
The simplest solution for both Ross and SMLEs was to have an Increased Chamber dimensions…that allowed for Mud fouling as well. The details are available in “The List of Changes”
Hence in Ross Rifles with “LC” chambers, a variety of "Ballooned " cases will appear…strangely, those in Naval Service seem to have been more conservatively “enlarged”…I have a Chilean DA (Naval) Ross, with Chamber LC marks, but the Cartridges show very little signs of Distortion ( about the same as a New Lithgow Barrel (SMLE)…and I use Prvi Military, Brit. Military, and Canadian (DIz) Military in my M1910… Both Factory new and Reloads ( neck size Only). NO Extraction problems…But then our range is Concreted and Well-grassed…NO Mud in sight, even after Tropical Rain…