Be careful with the slip on slings. My father used one on his shotgun one day to carry it 3 miles back a gated road turkey hunting. When he got there he got set up, he was disappointed to find it had rubbed a noticeable spot in the bluing on his barrel. (It didn't attach to the magazine cap).
I have a nice leather one that I carry rolled up in my turkey day pack. Slips over the barrel and then onto the butt stock. I only use it when I'm hauling a turkey out and it works really well for that.
Had it so long I couldn't tell you who made it or even where I got it...sorry.