I found a drawing in a book done by a British Officer of a Gurkha Soldier from the 5th Gurkha rifles during the Second Anglo-Afghan War, and the Gurkha was armed with a Brunswick rifle with a patchpox and bayonet. It looks exactly like the ones IMA has. I'm betting they chose these weapons due to the lighter weight and the terrain in Afghanistan. I will see if I can get a scan of the drawing. I don't think these were weapons issued to officers, but rather frontline weapons during this time for this reason.