I purchased a new CM9 a few months ago and have put about 500 rounds down range with it. The gun is flawless as long as I make sure the next round in the mag is seated to prevent the nosedive problems everyone seems to have. The issue is that this gun marks the brass fairly hard. I use this for ccw and as such it gets unloaded and reloaded more than usual. The brass shows scratch marks and even extractor nicks that are deep enough to catch your fingernail in. As a ccw gun I rechanber the same round more than once and it is pretty chewed up just from unloading/reloading. Do any of you guys know if I could polsh the feed ramp and back of chamber and get this to stop? I cant decide if it is scratching on the chamber or the magazine lip..... It is not a huge issue I realize but I hate seeing those cuts in my brass.

Chambering rounds more than about three to four times is something you should NEVER do.

In the early days of the police change over to the automatic pistol they had a rash of "Second round stoppages".
The officer would fire his pistol and the second round would fail to feed, jamming the gun.
This was traced to the police inspection procedure in which the magazine would be removed and the chambered round ejected.
After inspection the magazine would be replaced, the round in the mag would be chambered, the magazine removed and the first round replaced in the magazine.

What this meant was that the same two rounds were being chambered repeatedly day after day.
The bullets hitting the feed ramp were being pushed back into the case, causing the overall round length to be too short and the short rounds would fail to feed.
The short cartridges also cause chamber pressures to soar to unsafe pressures.

To eliminate the problem the police cartridge makers manufacture police ammo with tighter case crimps to limit bullet set-back and the police are trained to chamber a round no more then three to four times then either shoot the ammo in practice, or to discard it.
Commercial ammo is not loaded with the tighter crimps used on police ammo.

If you're chambering your ammo enough to cause scarring, you're chambering it WAY too many times for safety or reliability.
One way to check your carry ammo is to pull a new, unused round from a box of ammo and set it aside.
Use this new round as a gage to check your carry ammo for bullet set back. If you find a round with the overall length shorter than the new round, either shoot it if it's just slightly short or discard it if it's more than just slightly short.

As for sharp edges on the magazine feed lips, you can use a fine stone to LIGHTLY break the sharp inner edges of the magazine. Note "lightly". This will limit any sharp edges from cutting up the cases but can't prevent it since steel is harder than brass. Do more than just light rounding and you can easily ruin a magazine.

The extractor will scar the cases since it must get a good purchase on the rim to insure reliable extraction and ejection. If it's scarring the cases badly after one or two chambering, you should send the gun back to Kahr for correction.
You could try to smooth the extractor yourself, but make a slight mistake and reliability can be ruined.
Again, an extractor is steel and WILL scar up a brass case.

If the chamber or feed ramp is scarring the cases, something is WRONG, and the gun needs to go back to Kahr.

Bottom line, stop chambering your ammo so many times. This is not safe and will chew up the cases.
By repeatedly chambering the same ammo you're risking an unreliable gun as well as possible damage from soaring chamber pressures.
Also the chewed up cases are a reliability hazard.