Problems with Spikes new lower

[redwingshooter]

So I tried several different mags and had the same issue. I tried backing out the mag catch screw and this did not effect the problem either. I did, however, through the course of all of this discover what is going on. While playing around with the mag catch I discovered that there is some interference going on between the lower receiver where the mag catch rests. When I push on the mag catch with my finger there is a bit of resistance until I finally break it loose and then the mag catch moves freely. I'm planning on getting a better location of the interference and removing some material from the mag catch so the action is smoother. Any recomendations on tools for this job? Would a metal file do or do I need better tools like stones or something of the like?