Proven fact...a slung gun will cost you game.
Seems like all the Europeans (except the English) slung their doubles.
The English didn't need a sling because they mostly shot driven game from stations or either had someone tote their guns for them.
The common folk over there do a fair amount of "rough shooting", Joe. Walking up birds (and ground game) behind dogs. Also, especially early in the season, pointing dogs are used for grouse on the moors. Lots of walking, shooters carrying their own guns.
As far as driven shooting goes, much of it nowadays does not involve a stuffer/loader. You load your own gun. And you tote it in a slip (with a sling) when walking to your assigned peg.
Meanwhile, Stateside . . . my first classic sxs was a pre-WWII Sauer 16 with swivels and a cheekpiece. I found a narrow European sling for it. Comes in handy if you're going to snap a photo of the dog on point, retrieving a bird, whatever. And nice to sling arms when you're walking back to the vehicle with a limit in your vest. A sling works especially well for open country birds. Pheasants, huns, prairie grouse, etc. Grouse and woodcock, if you're in the thick and nasty, a sling can get in the way, hang up on stuff, etc.
