3.5" lead shot loads will HAMMER you, they are flat out NASTY!!!! Steel shot isn't nearly as bad, but it still isn't any cupcake fluffy load. Steel is like a 30-06, maybe a little worse. Lead is far and away heavier recoil than any 338 win mag I have ever shot, even seems worse than 340 weatherby.
I have shot several CASES of heavy target loads in one day from pumps and O/U shotguns, and shoot some hard kicking rifles. I have shot hundreds of patterns with 3.5" shotshells. I am not recoil sensitive at all, but I avoid lead 3.5" shotshells in a pump.
If you decide to try it make sure your mouth is closed firmly, it can chip teeth if you don't.