Prior to applying a good primer like Tamiya Metal Primer (see Category: TIPS-TOOLS/TAMIYA METAL PRIMER) or Tamiya Fine Surface Primer, I run a finger over all the visible brass model surfaces.  If I feel a burr or sharp edge, I take a fine-tooth miniature file and add a slight radius to take away the sharpness.  Paint or primer does not adhere well to sharp edges and would be prone to chipping.

This isn’t a bad thing to do for styrene or resin models either.