The full name was Rook and Rabbit Rifle.
W.W. Greener said the .22 "Miniature Rifle" was not well suited for a rook rifle, that it was too small for good killing of large rabbits yet had a long danger space when fired at a rook in a tree.
He said that the ideal would be a bullet that traveled in a flat trajectory for 100 yards... and then dropped straight to the ground. Unattainable to be sure, but a .295-.360 bullet of low ballistic coefficient made the effort.
No doubt standards were relaxed on expeditions to such benighted places as China and as late in the day of the Empire as 1935.
A friend has a beautiful little Martini actioned rook rifle in .22 LR. But the muzzle is circled by the telltale logo "Parkerifled". It has been relined from one of the real rook calibers to .22. I need to get him to make a search for proof marks to indicate which.