Where will you get the power from?the power can be generated on a simple principle. the same as bulet train is running. JUST TO UNDERSTAND AND SCIETIFICALLY NOT SO PRICISE.......... we have A.C. current electricity. it has up and down wavelength. + and - poles can be generated by electricity supply to magnet. suppose when the wavelength is upside, magnet has + pole and when down side, it has - pole. when a + pole of barrel comes near to - pole of the shell, it creates attraction between them. and the same time current passes through and wavelength is changing from up to down so - pole is generated. now the - pole of barrel comes behind the -pole of shell. which pushes the shell further outside the barrel.
infact, imo, it can generate more speed and can fire the shell at far distance means large range.