Since before 1912 Rigby were Mauser agents in the UK and managed to persuade Oberndorf to develop and produce special Magnum actions for them, other British companies who wanted to compete with their .400/350 Nitro Express big five game hunting rifles had to improvise and use standard-length Gewehr 98 actions, which only allow approximately 84 mm cartridges to fit into the magazine (a bonus was having a shorter bolt throw).
The round was the first in Great Britain (and the first major in the world[2]) to have a rebated rim, one that is smaller in diameter than the case body, an invention which Taylor patented in 1908.
[4] However, it complicated the magazine design: when the cartridge is pushed forward and the bullet rides up the feed ramp, smaller diameter rim dives down and tends to slip under the bolt face (especially in absence of special measures to ensure reliable feeding), which may cause a serious jam.
To solve this problem, Taylor developed (and patented in 1909[5]) a proprietary single-stack magazine akin to Belgian Mauser, which similarly extended below the stock.
[4] The rebated rim also allows government game officers and authorized hunters to use standard stripper clips for rapid reloads when culling rogue animals.