Moderators are occasionally referred to as silencers, but this is a misnomer as it's impossible to silence the report of a high-velocity bullet completely. ... It does not, of course, reduce the crack of the bullet, nor does it have any significant effect on velocity.

Does a suppressor affect velocity?

A suppressor will typically increase the muzzle velocity of ammunition and maintain if not improve shot group. The silencer is enabling the shooter to be more accurate by providing a much less violent platform to operate.

What does a moderator do on a rifle?

A moderator works by slowing and cooling the gasses emitted from the muzzle behind the rifle bullet. It cannot affect the 'crack' of a supersonic bullet breaking the sound barrier, but it can dramatically reduce the sound of the cartridge detonating within the barrel.