Picture available in “Sling Arms!” (1995), Geof Walden.
Keith Miller, Curator Weapons National Army Museum, London England. This was not a government issued sling and was most likely a private contract model sling that seems to have come around shortly after the Crimean War.
Weapons were purchased directly from manufacturers, who were free to attach whatever surplus or available slings they had on hand or make up their own. Steve Osman, Chief Historian at Fort Snelling and Fellow of the Company of Military Historians.