Bought a new Colt 9mm combat unit rail gun.
Have 600 rounds through it, no issue with function. When inserting a magazine, full or empty, it hangs up on the mag release. Even a good wack won't allow it to seat. Push the mag release in and it inserts. Figured it was something to wear in, sharp edge or something, but hasn't gotten any better.
Anything I can fix or does it need to go back?

I had a couple of the original Devel magazines that were reluctant to pass the catch. The metal was thicker than most and very square at the edge. I beveled them for easy insertion.

You could bevel the catch a bit more for easy insertion or try a different part.

First, I am presuming it is all the mags that came with the pistol.

Problem is that don't know whether it's the mag release, the mags or something out of spec in the frame machining for the mag release. Some suggestions:

1) Check the cut for the mag release on all of the mags. Burrs, irregular cuts, whatever.

2) With your finger, see if there are any burrs or excessively sharp edges on the mag release within the magwell. See if the mag release button requires an abnormal mount of force to fully release.

3) Lube the mag release around the external button and in the magwell. Lube the mag cut as well.

4) Borrow or buy another quality 9mm mag. See if it does the same thing. I you bought it from a LGS, you could bring the gun there. The dealer should have something to try.

If none of the above work, I'd send it back. It's abnormal and dosen't sound like any type of break-in issue. I presume it's still under warranty.

I do all of my own gunsmithing work and have played with 1911's since the 1970's. Even with my 1911 experience, If the above process came up empty, I'd probably send it back. Sure, I could pull the mag release out, disassemble it and check the components. I could also pop in one of my spare mag releases. My concern would be voiding the warranty though.

Something is obviously out of spec. Either the mag release, the mags, or the frame machining for the release.

Had an slightly extended mag catch do the same thing on my Colt.
$20 to my gunsmith and less than 10 minutes later it is happy to accept all mags.

Nuts!
Buggered up the screw taking it out.
Ordered another from brownells.
Give me a chance to polish it a little.

I think the two most common problems (aside from magazines) with 1911s are a poorly fitted slide stop and a a poorly fitted magazine catch.
A little tweaking will fix it.

Are you sure it's the mag release? (meaning if you push it, the problem goes away)

I've had minor issues like that, that went away with some shaping and polishing. Granted not something you want to, or should have to do on a new expensive gun.

The reason I ask if you're sure, is I bought a DW 10mm not too long ago that I thought was having the same issue. Turned out not to be the mag release at all though. (what it was might stray too far off topic as it's hard to describe)