You can use a spray gun with the Dulux range of chalked paints, but Rust-Oleum recommends a brush. This is partly because you'll lose some of the subtle nuances associated with chalked paints if sprayed. Brushstrokes, texture and the building up of layers won't be as noticeable with the sprayer, and you'll end up with a much more uniform finish. This might be the look you are going for. If you wanted the brushed effect and the convenience of the sprayer, you could have one person spray the paint and another following behind to lay it off with a brush. Doing a test section is always a good place to start.