[Master Assassin]

... Do I have to repeat that what could possibly, and actually, touch Touma first is the power bolt engulfing (and propelling) the speeding projectile and not the projectile itself? So when the power bolt touches Touma's hand it becomes "cancelled" - it loses all of its physical qualities: acceleration, velocity, momentum and kinetic energy - just like that.

But if you add the argument that even as the bolt dissipates into oblivion the projectile used for the railgun can still produce some hurt with the velocity and momentum it had left then I will concur.

Looks like here I can conclude why Misaka is fighting Touma in a very "unsmart" way (being as rash as she is): that everytime she unleashes an attack on Touma based on her powers, every single bit of her electricity that comes in touch with Touma's IB gets cancelled, thus fighting Touma was a great waste of energy (and time) unless she works her way out to get through that annoyance of a hand called the Imagine Breaker. Accelerator on the other hand gets his way easily just because he can use his powers to hurl some actual physical projectiles around to keep Touma under pressure. Note that even though the projectiles are hurled using Accelerator's power, they are moving with a velocity, speed and inertia of their own, enough to cause some real hurt.