I would never use a military weapon without a sling
It offers utility, a steady hold when shooting and is essential when you need both hands. I can't imagine hunting without a sling. How about when you plug a deer and need to drag him a mile or so? Or you need to negotiate a steep inline by grabbing brush and trees. If you were in the Army or Marines, you can have that weapon off your shoulder and in action in about 2 seconds. I even have a sling on my 10-22.
That is a very nice sling by the way. International Silver a mag company? They made magazines but I believe prior to that, they made practically all of the oilers. The only exception that I know of during WW2 was the SW Winchester. Post war, others made oilers.