I shot 3" winchester slugs during deer season. The only problem was that if I put in two 3 inch slugs last and the rest were 2.75" slugs; so when I loaded, one 3" slug would be chambered and one would be second in place with 2.75" shells following them. But when I was shooting at a deer, the first shot no problem, but the second 3" shell jammed. My first jam with my saiga-12. I stood there in a state of shock.
So, now I load just the first slug (the one that gets chambered) as a 3" magnum, the rest are 2 and 3/4... and problem solved. I have never tried gas setting #2, probably never