Shooting sticks and a bipod are better. Modern military snipers may learn to sling up (depending on the course they go through) but it isn't much emphasized, isn't considered terribly practical, and isn't much used out in the real world. At least one guy on the SOTIC committee in the SFG I was in was pretty outspoken about advocating that even the Level 1 course at Bragg de-emphasize the NRA-influenced portions of their curriculum, including use of slings, to concentrate more training hours/days on things guys are actually doing downrange like sniping in urban/built up terrain.