This is a strictly ' For What It Is Worth ' comment.
During LRRP training, we were given a multitude of different weapons to fire. Our instructor suggested taking a couple of magazines and just blasting through them in very reapid semi auto fire. Then, pop in another magazine and shoot at a more normal pace. It really seemed to help in getting familiar with a weapon.
Who knows why?? But it worked for us. probably because we were so brainwashed he could have told us to shove the guns up our butts and do the same thing, and we would have.