It's worth reading the link above, but the short answer is that a suppressor by itself reduces recoil by adding additional weight to the rifle at a location that's very helpful. Now, many suppressors can be mounted on attachments that have real brakes themselves. In that case you have both the benefit of the brake and the additional weight at a helpful location. That's the best of both worlds, at least I think so. I have a Griffin Armament Sportsman DT on a .30-06 and it's great, but it's nothing like my Griffin Armament Precision Hunter over a brake on my .338 LM, which takes a light .338 LM and makes it feel like a .308.
NRA Endowment & DSC Lifer