It makes a bit of a difference on the Enfield/FAMAS/AUG but pretty much no difference on the Galil/Commando/AK47/M16.
The reason is the FAMAS/AUG/Enfield are 35/25 guns in terms of damage. In hardcore, players have 30 HP, so the silencer may make more of your shots take an extra bullet.
With the Galil/Commando/AK-47/M16, they are all 40/30 guns. So, even with the silencer, they should be doing enough damage for a 1 hit kill at any range in most cases.