Yes, of course there is an upper limit, the device is chucking something with mass out the end. It takes energy to get it up to speed, there are things like air resistance, rail friction etc. Take it into space to solve the latter. The military are using rail guns now, and are finding that the rails supporting the ejected mass are getting to very high temperatures, and wear out rapidly.
My question was to vague. I see that now. What I should have asked was "Does a railgun or a LIM have the ability to impart more force into the projectile before limiting factors due to electromagnetics come into play?"
