It strikes me as somewhat odd that a carbine for officer's military use would feature a 5 or 6 round magazine, though of course a 10 round mag could easily be substituted "on active service". Perhaps a 10 round mag was thought to be too close a resemblance to the service rifle? Of course the whole idea of an officer carrying a rifle or even a carbine was somewhat questionable even after the Boer War: officers were there to lead, not to actively fight so the thinking went.