I was wondering if some of you had techniques to improve magazine feed.
I seems people are filing and polishing the lips to prevent them from catching or rubbing excessively on the bullet tip and or case.
What do you do?
Thanks.

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Your magazine shouldn't need improving.  If you're having to modify something to get them to work they are junk.

New magazines should be returned to the manufacturer for replacement if they have issues.

Used magazines, really old ones, can use replacement springs.

I have Colt (NHMTG/OKAY) magazines from the 1970's that still run 100%, the only one that ever gave me trouble was the one I tried to "improve" with a new anti-tilt follower.

I agree, I also have older 20rd Colts which I use at the range.
The background of my question, was to apply fixes towards 6.5 Grendel mags, many of which have issues (catching bullet or case). I assume adjusting the lips a bit would help on lightly polishing the front of the mag?

I have has lots of trouble with Grendel mags too. These are some of the things I did to smooth them out.

Disassemble and clean, followed with sprayed with silicone lube.

Debur any flashing on the followers.

Use a Dremel or hand file and remove a half-moon cut out right where the magazine mates with the barrel extension. This allows clearance for the fatter 6.5/6.8 bullets to enter the chamber without dragging against the magazine body when being fed.

Using a fine/medium stone dress the top of the magazine lips to remove the sharp edge. Do the same to the interior edge where the bullets ride. All you're trying to do is eliminate the knife edge so the magazine lips don't cut into the cartridge cases or against the bcg.

Reassemble the cleaned and lubed magazines.

Load the magazines to capacity and allowed them to sit loaded for one (1) month. Remove one round then allow the magazine to sit for one (1) more month. This allows the loaded magazine to "tease" both magazine lips to conform the the shape of the cartridges.

Do all these things before trying to forcibly bend the magazine lips into compliance. Aluminum does not like to be bent. Steel can take it, aluminum not so much.

All AR-15's shooting cartridges with bigger cases than 5.56mm/.300 blackout can benefit from modifying the ejector. Robert Whitley's www.6mmAR.com website has a tutorial. I prefer the rounded and polished ejector pin head to the ground angle option simply because you can't screw it up.

If all of these tweaks fail to work, then and only then do I try to bend the feed lips to change the angle. Remember, if you raise the front of the feed lips you will lower the rear of the case head. Do it too much and the bolt will ride over the cartridge, instead of stripping it from the magazine.

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I replace USGI followers with Magpul followers, these makes them feed much more reliably

borderpatrol: Thank you!