can a rail gun be converted into a "High Velocity Pulse Engine",to be used as a "Jump Drive" to achieve light speed capabilities.
No. Railgun could be used as a common reaction engine with specific impulse of order of 700 seconds, which is a respectable number but nothing coming anywhere close to relativistic velocities and already worse than existing ion engines. There's nothing in the concept of the device that could suggest it could be made it into a 'jump drive'.
In my opinion it would not be practical to use it anyway. Please correct me if I am wrong: In my oppinion the terminal velocity is not as big issue as the time period over which we need to build the momentum. If human body cant take more than 1,2 g in the long run it is not practical to build engines that can accelerate faster than that. So the question is which drive is the most efective to achieve acceleration of 1,2g for longest periods of time. But that is just my opinon. I will be happy to discuss.