It is fairly common to see cylinders with some pretty tough carbon deposits right in the chamfer where the case mouth stops. Removing this "moon rock" can be difficult at times. Leaving it to build up will eventually cause rounds not to seat fully and can impede the bullet pulling crimp and opening the case all the way to release the bullet.
Some of these carbon deposits can be removed fairly easily, but every now and then you get one that just defies every attempt to have this area clean and shiny. Here is one that a customer sent in to have the throats reamed and honed to .4525" and in the process of trying to remove the carbon with a dremel tool and a small, very stiff stainless steel cup brush, I discovered each chamber had a ridge or "corn row" as I called it, which gave the carbon and some leading a perfect place to perch and after a more than difficult effort to remove the carbon, I finally got down to the ridge which we decided would be best served by having the chamber reamed with a finishing reamer, which worked great for removing ONLY the offending metal in the chamber, while keeping the rest of it perfectly smooth and shiny.
This cylinder isn't bad per se, I have seen them with a LOT more carbon buildup, but here's what it looks like:
After laboriously removing the carbon, the reason it is building up in the first place is revealed, a solid ridge of metal all the way around each of the chambers:
After using the Clymer 45 Colt finishing reamer, the ridge is gone and this cylinder should be very easy to clean in the future as there is no roughness or ridge for carbon to cling to and build up:
Some of these carbon deposits can be removed fairly easily, but every now and then you get one that just defies every attempt to have this area clean and shiny. Here is one that a customer sent in to have the throats reamed and honed to .4525" and in the process of trying to remove the carbon with a dremel tool and a small, very stiff stainless steel cup brush, I discovered each chamber had a ridge or "corn row" as I called it, which gave the carbon and some leading a perfect place to perch and after a more than difficult effort to remove the carbon, I finally got down to the ridge which we decided would be best served by having the chamber reamed with a finishing reamer, which worked great for removing ONLY the offending metal in the chamber, while keeping the rest of it perfectly smooth and shiny.
This cylinder isn't bad per se, I have seen them with a LOT more carbon buildup, but here's what it looks like:
After laboriously removing the carbon, the reason it is building up in the first place is revealed, a solid ridge of metal all the way around each of the chambers:
After using the Clymer 45 Colt finishing reamer, the ridge is gone and this cylinder should be very easy to clean in the future as there is no roughness or ridge for carbon to cling to and build up: