User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-7336553-20130412001801/@comment-5043481-20130412165701

It decreases the time you cannot move for after firing, so you can get more shots in in a certain amount of time. Especcially the powerful crag/clust and lvl 3 pierce/pellet shots, as they have large recoil, but all types are affected.

I don't think it affects rapid fire rate.