The entire story is in "The Temple Tiger" which also has descriptions of his Jones under lever .500 Modified Cordite DR.
I was wrong about the trigger being of a military type. Corbett stated that the Manton's manager had told him that the trigger had a double pull off and that he (Corbett) was not familar with this so-called improvement and did not know it was necessary to pull the trigger a second time after taking up the initial slack.