Barrel Fouling

By: Daniel Lilja

This article was published in the March, 2000 issue of Precision Shooting Magazine. It was written as a respose to a query by Editor Dave Brennan in reference to a rifle barrel fouling article written by Fred Barker which was published in the February, 2000 issue of Precision Shooting. DL

I read the excellent article by Fred Barker on fouling and accuracy in his 6.5 caliber 1000-yard type rifle. Per your request I’ll do my best to convey my thoughts and observations on rifle barrels and bullet fouling.

It has been my experience in shooting a number of rifles and barrels used in 1000- yard rifles, that longer barrels and faster twists tend to foul more. And as Fred pointed out, this could be caused more by the long bullets (and the internal forces acting on them) than the barrel. I found too that some bullets just seem to foul more than others. This is no doubt caused by differences in the gilding metal used to make the jackets.

Fred makes some important observations and distinctions between true high-quality custom barrels and production barrels. I liked and agreed with his comment that ” . . . in poor quality, mass-produced barrels, that build up thick, rough fouling and shoot poorly, every shot is a flier.” One of the big differences between these barrels is the internal finish. A rough barrel is going to foul. After looking at the differences between a production barrel and finely finished lapped barrel in our video borescope, a customer made the comparison that the production barrel looked like railroad ties and the lapped barrel like a mirror.

Makers of custom hand-lapped barrels spend a lot of time achieving the internal finish that they require. We’ve experimented with different techniques and products and have settled on what we believe gives us the best finish. We strive to get a smooth uniform finish without losing the geometry of the rifling — that is, keeping the lands sharp-cornered and crisp. And though it may surprise some, lapping to a finer finish will result in an increase in fouling. A barrel can be too smooth.

We’ve had customers ask about aftermarket operations and procedures that will “improve” the interior finish of our barrels. And I always warn them against it. The thought of lapping with 1200 grit makes me cringe. And I also feel it is very desirable to have the direction of the finish lay parallel to the rifling. A finish like this is produced naturally with hand-lapping. Some procedures can and will produce a directionless finish. My advice is to leave the internal finish to the barrel maker. Trying to “improve” it is only going to make it worse. The exception being unlapped production barrels.

I’ve noticed too that given an equal interior finish in both stainless steel (416) and chrome-moly (4142), the chrome-moly barrel will copper foul more.

I have not seen any real reason to use a dry lubricant on bullets as an effort to reduce fouling. With a proper barrel break-in, a top quality lapped barrel, and normal cleaning procedures, fouling just does not appear to be a major problem. We have now available some excellent bore cleaners that do a great job of removing the powder and jacket fouling that does accumulate. My personal favorite is Butch’s Bore Shine.

It is important to break-in a barrel though. The jacket material must be removed after every shot during the initial few rounds. If this isn’t done the areas of the barrel that fouled will tend to pick up more fouling and it will build on itself. It is important to get a layer of powder fouling on top of the lands & grooves. This hard deposit will prevent the copper from stripping off the bullets. However, if the internal finish of the barrel is too rough the barrel will never be completely broken-in and fouling will always be a problem. Some barrels can’t be broken-in.

A similar phenomonon can exist if the shooter uses an abrasive-type cleaner too often. The abrasives are very effective at removing all traces of both powder and jacket fouling. I mentioned that a barrel can be too smooth. The abrasives can get a barrel too clean as well and in effect the shooter is rebreaking-in the barrel again every time he cleans. This can end up in the dog-chasing-his-tail scenario. The shooter thinks the barrel is a fouler, as evidenced by the copper accumulations in the barrel. He works hard at removing the copper, resorting to using an abrasive cleaner. But when he does he removes the desirable layer of carbon fouling left by the powder and exposes fresh steel ready to grab some more copper off the bullet on the next shot. The cycle repeats itself. Like the dog the best way out is to go lay down and take a nap.

I don’t think I agree with Fred that the elements added to the steel to aid in machinability are a problem. At least for the steels we use. We buy our steel directly from the steel mills in truckload quantities and specify the chemistry we want. It is rare to see imperfections in the steel caused by impurities or alloying agents. And if they do show up as blemishes in the lapped finish, I would consider their size insignificant.

I do agree with the premise of Fred’s article; we don’t know all there is to know about fouling in barrels. But I do think that some of the procedures that have been tried and are still used by many shooters are steps in the wrong direction. Dry lubricants, surface finish enhancement procedures, and the overuse of abrasive cleaners all fall into that category, in my opinion.