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Copper Fouling

This article is provided by RSI as an instructional aid. If you have never used cleaning solutions other then those that come in cleaning kits, this article is especially for you. You may be doing everything possible to achieve a perfect rifle load but if your barrel fouls too quickly your effort is wasted.

Let's start with the basics.

1) For the purpose of this article we are addressing only the most common form of fouling caused by copper left in the bore from bullets fired with smokeless powder.

2) It takes several shots to first heat then "foul" a cold clean barrel so velocities stabilize and optimum accuracy can be achieved. This is because initial shots through a clean barrel produces different frictional energy until lube is blown out and the bore is coated with powder residue and/or copper so bullet friction begins to stabilize. The following pressure trace taken from a bench rifle shows what happens when starting with a cold clean barrel. The trace happens to be for a moly bullet load but the same phenomenon is evident with bare copper bullets.

Barrel Fouling

And the copper keeps building up! Soft metals gall and stick to similar metal. Each round fired through the barrel will deposit a little more copper until accuracy deteriorates. Once a barrel is fouled successive shots will not remove the copper.

3) When copper fouling becomes severe, bumps of copper above the bore surface create restrictions that "tear" the base of the bullet jacket as it passes down the barrel. This adds air turbulence at the base of the bullet and is detrimental to consistent flight.

4) All barrels foul. It is simply a matter of how many shots are needed to first stabilize velocity then how quickly it fouls so severely the rifle starts "tossing flyers". Obviously if it takes nearly 10 shots for velocities to stabilize and at that point the barrel is fouled so severely accuracy is impossible, you have a problem. The barrel is called a "fouler".

5) Copper is easily removed with a good copper solvent. Ammonia has been the chemical of choice for removing copper from barrels for over 100 years. To my knowledge there is no detrimental affect from using an ammonia based solution providing it is thoroughly removed before the arm is stored.

We are not fans of electronic cleaners because the don't address the root cause of fouling. Electronic cleaners can etch the bore if left running too long and we are concerned those who rely on them may eventually damage their barrels. If you use an electronic cleaner, make sure you follow directions carefully and do not "over cook" your barrels.

Fr. Frog has tested various copper removers, for more info click here. Of all the copper removal products on the market we believe KG-12 from KG Coatings is one of the best. It was originally developed for military artillery systems, is extremely aggressive but does not affect the barrel steel. There are now other similar products available such as Wipe Out which offer advantages in dry climates where it is difficult to keep solutions wet in the bore. The good 'ol ammunia based solutions (Sweets) do have one distinct advantage in that they allways provide a good brite blue indicator of fouling.

6) New commercial barrels may foul horribly after only 10 shots. Even new custom barrels may foul badly after only 20 or 30 shots. Both can be improved. Here's how.


First the barrel should be new or cleaned thoroughly of all copper down to bare steel. Shoot a round and use an ammonia based copper solvent or KG-12 as directed by its manufacturer. Most instruct you to first run a patch wet with a powder solvent such as Hoppe's no. 9 through the bore to remove powder residue, then a dry patch so you are down to copper. Then pass a patch wet with the copper solvent thru the bore and wait a few minutes repeating this last step until no copper residue comes out on the patch.

Repeat this process until after a single shot there is no copper residue on the first patch wetted with copper solvent. Then go to two shots at a time, then three, etc. Ideally you will want to be able to shoot at least 10 shots before you get copper deposits from the bore. This should allow at least 15 to 20 shots before there is sufficient copper fouling to "Toss Flyers" and velocities should stabilize quicker when starting with a cold clean barrel. It is a time consuming process and may take an entire day, but the effort is well worth it. Eventually the gun will clean with just a few patches and no "scrubbing" with brushes will be required.

NEVER use a stainless brush and if you must use a bronze brush, push it entirely through the barrel from the chamber end in one complete motion. Do not pump the brush back and forth. ALWAYS use a bore guide so you do not wear rifling in front of the chamber.

Why This Works
No matter how a barrel is manufactured there will be microscopic holes in the crystalline structure of the steel. Copper will collect in these voids. Because like metals tend to "stick" to like metals, more and more copper will accumulate until the fouling material is higher then the surface of the bore. This is when accuracy will seriously deteriorate and you feel the roughness when a tight patch is pushed through the barrel. Copper solvent removes the copper from these voids so each successive shot can "slough" surface molecules into/over the voids until they are nearly closed. The result is a smoother bore and much less fouling.

Top shooters never pull a metal brush backward through the bore and will only use a nylon brush (to remove powder fouling) and patches. You should never need to clean a good barrel with a metal brush!

Yer Ol' Huntin' Guns
If you have never owned a barrel cleaner other then the junk that comes with most cleaning kits you may now know why that old hunting rifle no longer shoots like it once did. It may just be severely copper fouled. Clean the copper out and it may shoot factory ammo like it used to. And, if you work up a good load... it may even shoot half inch groups!


The ingredients in most bore cleaners are well known and it is easy to mix your own solvents that will work as good or better than many commercial products. Fr. Frog has provided great information for people interested in trying various home made cleaning solutions.

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