acceleration in a hypothetical railgun is not small, it is huge...
don't say small or huge. it depends on how much power you feed in. in fact you can make it as small or large you want it to be. (provided you have enough power for the electromagnets).

Its speed cannot increase much higher. The shell could be burned out if the gun weren't. And I doubt if there is a possibility to fix any guidance system on it.
to build a working model