Cato, the internal mechanism doesn't really matter due to conservation of energy. That energy must come from somewhere. Were does it come from? Energy lost to friction, sound, or light? I think it improbable that some of that energy doesn't come from the bullet, or blanks would cycle just fine.
No one is saying that the energy does not come from somewhere. Obviously energy is used to cycle the action. There is a lot of energy from the powder that is not used to propel the bullet. There is wasted energy that you can feel as heat on the barrel. There is energy is used to cycle the slide. More wasted energy transferred to you hand and arm etc. The energy used to cycle the slide is why perceived recoil is less on a semi auto.
My comments and explanation are strictly related to the question asked by the original poster.
Again, this is unnecessary detail due to simple energy conservation, but I don't see how this could be correct. My understanding is that movement of the slide-barrel-cartridge system relative to the barrel link unlocks the barrel once the bullet is away. That is, the barrel unlocks once pressure is low, not because pressure is low. That is, while the bullet is still in the barrel, the locked slide-barrel-cartridge has already accelerated, even if it has only moved 1 millimeter
You seem to also under the assumption that the barrel cycles. It does not. If you are saying that the slide and/or barrel has moved one millimeter because of the loose parts on a semi auto as compared to, lets say, a Thompson Contender then I think you are being picky. For all practical purposes, the slide does not move until the bullet has exited.