If you've always believed that 'fouling' is something that only occurs on basketball courts, then this is the article for you.

Within the context of today's column, the term will refer to the residue that accumulates in your gun's bore after firing one or more cartridges. While it will certainly come as a surprise to no one that the interior of a pistol, rifle or shotgun barrel becomes dirty (fouled) upon firing, the exact nature of the fouling materials and their effect on the accuracy, function and useful life of the firearm may not be well understood by the average sportsman.

To put this information into context, let's stop for a moment and try to imagine the sequence of mechanical and chemical processes, which come into play during those few brief milliseconds between the time you squeeze the trigger and when the projectile exits the muzzle. If you do, you'll have a pretty fair idea where all the 'crud' comes from.

Disregarding any foreign material (dust, dirt, water) entering from the muzzle or an open breech, there are three primary sources of barrel fouling. First on our short list of culprits is the primer. That's the innocuous-looking metallic sphere resting in the center of the cartridge base on centerfire (hence the name) and shotgun cartridges. It's really nothing more than a metallic cup that sandwiches a powerful and highly flammable compound beneath a wedge-shaped anvil. When struck with sufficient force by the firing pin, the malleable primer cup indents, capturing the combustible primer pellet beneath itself and the pointed anvil. Pressure and friction ignite the mixture, sending a blast (and I mean a blast) of superheated flame and particles into the powder charge perched atop it. "NASA, we have ignition!"

Thanks to the miracles of modern chemistry, the contribution of today's primers to barrel fouling is admittedly slight - not even in the same universe as the debauchery committed by their predecessors of by-gone days - the corrosive primers. These 'renegades of rust' plagued generations of soldiers and sportsmen by depositing a smattering of potassium chloride salts in the barrel's interior with each firing. Potassium chloride, like its kin - sodium chloride - has a great affinity for drawing moisture. If not promptly removed by conscientious cleaning, the barrel would soon scold its owner by taking on a rich, reddish-brown shroud of oxidation; a real detriment to the longevity of barrel steel.

The primer's heat energy blasting through the flash hole instantly converts that neat pile of nitroglycerin and cellulose granules - otherwise known as gun powder - into a tremendous volume of superheated, rapidly-expanding gases. Much more gas than can possibly be contained within the limited confines of a cartridge case.

Unable to restrain the escalating pressures produced by that rampaging vortex of gas molecules, the cartridge casing swells - conforming to the dimensions of the firearm's chamber. The rampaging gases ravage the brass or plastic shell casing seeking release.

The weakest point (hopefully) proves to be at the end of the casing, which is capped only by a bullet or shot charge. With an escape route secured, the continually-expanding gases roar out of the casing and down the barrel pushing the projectile(s) ahead of them.

The loud "Ka Bang" we hear when a shell discharges is produced by the sudden squirting of the main gas column into the atmosphere when the bullet pops from the muzzle. This is exactly like the 'pop' generated when you uncork a bottle of the 'bubbly.'

To commemorate their passing, the powder gases foul the bore with the offspring of their combustion - a stubborn clinging residue of carbon, nitrates, and graphite particles. Each succeeding shot further aggravates the condition by pressing one more uneven layer of contamination atop its predecessors. Though all firearms are generally a "rule-unto-themselves," and vary in their sensitivity to this buildup of contaminants, the optimum accuracy potential of most high power centerfire firearms tends to 'sour' after 20-plus rounds. Obviously, smooth, high quality barrels will foul less than their less costly brethren - blessed with an abundance of machining tool marks and dimensional imperfections.

Now if I've managed to hold your attention thus far, bear with me for the 'worst' is yet to come. Far and away, the most sinister villain of barrel fouling is the projectile itself. Its composition, hardness, and the speed it is pushed through the barrel all combine to determine the amount of fouling left in its wake.

But, alas, that 'dirty' tale must wait for another day. Be sure to tune in to my next column, where I'll not only discuss the nasty contribution that the bullet itself makes to your barrel's fouling, but I'll also highlight some 'miraculous' modern cleaning chemicals that make 'short work' of even the 'foulest of fouling.'

Till then, happy shooting.

Rich Simpson may be reached at rsimpson29@hotmail.com.