Has anyone done this?  I was just looking at the two feed ramps in my upper today and they looked smooth but could be done better.

I'm sure I'm not the only one who has thought about this.

i did it on my colt a few years ago and i didn't notice much of a difference. i think it doesn't make as much of a difference with a rifle as it would h 45 or other handgun throwing a flatter, stubbier projectile, i jus used some flitz and 1 trillion grit sandpaper and POLISHED it a little., just like a handgun.  u know, my bushmaster shorty for some reason puts deep scrapes on the bullet when i cycle loaded rounds manually AT THE RANGE IN A SAFE MANNER, i wonder if this is the extractor action or if it's happening when it's being loaded into the chamber?

Unless you have a bur that is leaving a scrap mark on your brass, leave the ramps alone.

The only mod that you may want to think about is installing the M-4 cuts to the receiver and ramp.  On some rifles, running non-standard ammo, the round will hit just below the feed ramps and cause a jam. This will solve the problem.

But that takes us back to:  If it's not broke, then don't fix it.  

I have to agree with the "if it ain't broke don't fix it analogy" but if you feel the need to polish your ramp be careful with sandpaper.  For all of my polishing, I use bore paste and a dremel tool fitted with felt polishing wheels.  I've polished feed ramps, pins, trigger and hammer contact surfaces, etc.  One would be surpised how smooth a factory trigger can be made by just a little polish and Militec re-lube job.  Granted that bore paste won't work when material actually needs to be removed but it does a wonderful job polishing hardened surfaces without damaging the hardened coating.  Although it takes time to get results, you don't have to worry about removing too much metal or galling up the surface like you do with a stone or sandpaper.  After I get a mirror finish with bore paste, I clean my parts of any residual paste and/or lube with a good solvent, use a different felt wheel, apply a couple of drops of militec, and polish again.  Many people don't realize that heat and friction are needed to make Militec do its magic - the felt polishing wheel easiliy accomplishes both.  I used this procedure on a Sig P226 feed ramp that was too rough for my liking and it worked great.  The same thing was done to a recently installed Accuracy Speaks trigger (which are EDM cut from hardened stainless steel) that had a small bur on the face of the engagement surface on the trigger - now it's as smooth as silk and breaks great.