So there you are with a bore that’s free of powder residue and a sickly smile on your face, and it’s time to get down to the real villain, which is copper residue. Powder fouling is unattractive, but pretty much harmless. Copper residue will take away your barrel’s accuracy and wreck your barrel in some cases.
Various bullet makers claim that their slugs are less likely to foul because they’re copper alloys, or because they’re pure copper. No, sorry. Everything fouls. If you look down your bore in good light from the muzzle end, you’ll probably see copper. If you were to look at the grooves and lands with a borescope, you’d see streaks and lumps of it all the way back to the lede, which is the rear edge of the rifling. If you leave copper in a steel bore in a humid environment, it will eventually pit the steel. What it will certainly do is remove your barrel’s ability to shoot accurately.
If you look down a bore with the naked eye and it appears bright and shiny, that means nothing. I will bet you the fee for a Bill Clinton speech that there’s copper down there. There are two ways to detect it: First, run a patch with an ammonia-based copper killer such as Sweet’s 7.62 or Barnes CR-10 through the bore. If it comes out with blue or green stains, you’ve got copper. Or, use a somewhat less violent chemical such as Hoppes Benchrest or Shooter’s Choice and let it sit an hour. Then run a second patch through. If it comes out blue or green, it’s copper.
Or get a Hawkeye Bore Scope. The Hawkeye costs about as much as a good rifle scope, but long after you forget what you paid for it, you’ll wonder how you got along without it. He who lacks a Hawkeye is working blind.
So, you’ve got copper. How do you get rid of it? There are three ways: First, let the bore soak in Shooter’s Choice or Hoppe’s, muzzle pointed slightly down, until green gravy collects at the muzzle. (By the way, put a newspaper under the muzzle. Dissolved copper makes fabulous stains). Run another wet patch through, and repeat as needed. This process works most of the time, and does not involve elbow grease, but is very slow. It can take days to get the job done completely, and there are cases of copper fouling where it has no effect at all, and I have no idea why.
Or you can use the two ammonia-based copper killers I mentioned earlier. Use them in the garage, AND DO NOT LEAVE THEM IN THE BORE FOR LONGER THAN THE DIRECTIONS SAY; THEY WILL PIT YOUR BARREL. I speak from experience. Do not put copper killer on a bronze brush. Bronze is a copper alloy, and the ammonia will eat it. This method is much faster than the powder solvent route, but again, there are some cases of copper fouling that it won’t budge, and I have no idea why.
Third is the one I use: J-B Non-Embedding Bore Cleaning Compound. It comes in a little white jar, and is a mixture of grease and very fine polishing rouge. It requires elbow grease, but it always works*, and works best in combination with a penetrating oil called Kroil.
First, run a Kroil patch through the bore. Then screw a worn out brass bristle brush on your cleaning rod and wrap the brush in a square 12-gauge patch. The thickness of the patch is determined by the bore diameter. What you’re after is a snug fit. A bigger or smaller brush may be required, or you may have to trim the patch to get it right. Whatever it takes.
Now, put a blob of J-B on your finger and work as much of it as you can into the patch. (You don’t want the stuff getting in the chamber and the action.) Push it slowly forward until it starts to emerge from the barrel. If you shove the patch all the way out, it will unravel and you’ll have to unscrew the brush, pull the rod clear, and start all over again.
So, back and forth, in and out. I give it 30 strokes (counting one way). You may want to do more, or less. Each barrel requires different treatment. When you pull the patch out, it will probably be black, with pitch-black streaks where it was contacting the lands.
At this point, get all the J-B out with powder solvent and leave the bore wet for a couple of hours. Put another wet patch through and see if it’s green or blue. If it is, you’re not done yet. I have rifles that require four and sometimes five J-B patches after a day at the range. You’ll never get the J-B patches to come out clean. They’ll always be fifty shades of gray, or black. This doesn’t matter; all you’re interested in is clearing out the copper.
So, once all the J-B is out of the bore, run an oily patch through it (Rem Oil is good for this.) and then a dry patch. All you need is layer of oil a molecule or two thick. If you leave more, it will eventually run into the action or the stock. Wipe out the chamber, wipe off the bolt with an oily patch, and you’re done.
A note about oil. If you have a stainless barrel, or if you’re going to shoot the rifle next day, don’t bother with oiling the bore. But, if you’ve used either of the ammonia copper killers, you absolutely must oil the bore. Ammonia will suck every last living bit of lubrication out of the steel, and may cause the bullets to gall as they pass down the barrel.
There is no single “correct” way to clean a barrel. This is what I’ve come up with over the years, and there are infinite variations on it. On the one hand it’s a lot of work, but on the other, I’ve never had a barrel die from neglect.
*J-B becomes difficult to use if you leave it in the cold since it stiffens up like hardened putty. Store the jar indoors or tuck it into your armpit. If you do this, you’ll develop a strange, lopsided appearance that will repel some people and attract others.