Saskbooknut,

The Murcott was a lever cocker, and hence not fast enough for driven shooting. The boxlock brought along barrel cocking, increasing the speed of loading. Speed was important in driven game shooting so guys like Lord Ripon could manage 28 pheasants per minute!

Arguably a lever cocker is more suitable for modern walked up hunting, which probably explains the popularity of lever cockers such as the Ideal and the Darne in France.