According to White & Munhall, Pistol and Revolver Cartridges, your round is a .230/.297 Morris Long. Its length should be 0.787 - 0.827 inch. The short version is 0.583 - 0.584 inch (pretty tight tolerances, but that’s what the book says). The cartridge is also know as the G.R. 400, 5.6 x 20 Morris, 5.6 x 20 Revolver, and 5.7mm Long Morris. According to the authors, both the long and short versions were fired in guns with the same chamber dimensions, the longer version having more powder for higher velocities.
I’m sure the British collectors can add more.