I would guess that you've still got some "unremoved" metal within the end of the mag tube that is restricting movement of inserted rounds. The most normal problem here, when removing those damnable indentations that Remington insisted on adding, is failure to completely (and uniformly) remove all evidence of restriction.
More people get in trouble with Dremel tools and guns than any other combination of working tools I can think of. What you need to do is assure concentricity of the inside of the mag tube, something difficult, but not impossible, to do with a hand-held grinder. An adjustable reamer, set for the proper I.D. of the tube, would set up and maintain concentricity. Lacking such a device, a simple brake hone might also be used for the purpose, albeit with a major judiciousness in its application: Wouldn't take much with a hone to screw up and go through the thin walls of the tube.
Bottom line is that this really is something that can be done by the average home 'smith with the average shop tools, but it takes going low and slow for a while, trying and fitting until your shells are free within the tube. You can actually do it properly with your Dremel, just so long as you manually feel for high spots, relieve those as encountered, and proceed slowly and carefully. Best of luck.