TKDonuts

While I personally do not have a degree in electrical engineering (since I am only a student right now), I would have to say that a coilgun style of plunger acceleration would be highly inefficient, and very impractical. My knowledge of this stems from my personal experience building my own coilgun.

 

First of all, the weight of the projectile that a coilgun fires is minuscule in comparison to what your plunger rod would have to be. Additionally, the deceleration forces that the plunger would be experiencing (i.e. air resistance, friction, etc.) would likely be to great in comparison the the forces that would be exerted by the electromagnet. It is important to remember that the air resistance and friction on a coilgun projectile is relatively small, while an actual plunger has to push a lot of air to be effective, and have will have a lot of friction with a relatively large plunger diameter. 

 

Second of all, again from my experiences building a coilgun, the amount of voltage and current required to power a coil to accelerate a 1" long nail (the projectile I used) to the speed where it could start to break things is incredibly dangerous. Luckily for me, my dad is an electrical engineer, and he helped to prevent me from killing myself, however to the inexperienced, this could be incredibly dangerous. To power the coils, you would need to us a large capacitor which is (a) very dangerous and ( would require time to charge between each shot. Like I mentioned before, this will still not have enough power to accelerate a plunger rod. 

If you were designing the pump action style grip to balance the stress then you could probably put the pump action grip on the top of the blaster (like a recon) instead of the bottom, as that would balance the prime of the blaster in the same manner as a pump action style grip, however it might make the longshot look a lot worse, and have a slightly lower rate of fire then a pump action grip.