Ever since getting a Teslong bore scope I've noticed that several of my rifles with factory barrels seem to get the worst copper fouling in about the last 2-3" before the muzzle. I've seen this now in a 22" barrel (270 Win), a 24" barrel (also 270 Win), and a 26" barrel (257 Weatherby). I seem to recall my 18.5" barreled .308 doing the same thing, but I'm not certain on that one.

What gives?

Does this have to do with proximity to the muzzle per se, or more to do with the distance the bullet has traveled in the bore? My observations so far seem to support the former, since it seems like it's a consistent 2-3" from the muzzle regardless of barrel length. But I admit I haven't been taking close measurements.

Could I be doing something—e.g., in my cleaning regimen—that exacerbates this phenomenon? Not that I really have "a cleaning regimen." I do something a little different every time depending on what and how much comes out on the patch. But generally I use Patch-Out, Montana Copper Killer, and JB paste as necessary.

Any insights would be welcome.

I believe there's a slight taper in the bore of most, if not all, barrels. The small end goes toward the muzzle. Factory barrels are not finished as well as customs... think 80 grit vs 400 grit (an exaggeration).

Frictional heat would be the worst there as well I imagine.
GreggH

This--velocity's fastest near the muzzle.

While some bores are slightly constricted near the muzzle, those of most factory barrels aren't.

Might also add that often more jacket fouling occurs just in front of the chamber, but can also occur anywhere through a rifle's bore.

The bullet speeds up closest to the muzzle. There is more friction at that point is why there is more fouling nearer to the muzzle.

So can I conclude lower velocity cartridges tend to produce less jacket fouling, all else being equal, than higher velocity cartridges?

Not necessarily. It depends on the bullet and powder used, the quality of the bore, etc. etc.

What you're going through is what every new bore-scope user has for decades. Along with finding out there are no absolute rules about where bores foul most, you'll also eventually "discover" that visible fouling doesn't necessarily affect accuracy.

Trying hard not to place undue weight on this new stream of data, but some of the things I've seen through that scope are pretty hard to ignore. For one, how rough some factory bores look under magnification. The lands look like a damn rumble strip on some of them.

If nothing else, it's given me a much greater appreciation for hand-lapped barrels.

I've heard more than once that minute copper particles broken free with the bullet moving through the throat are vaporized, carried and re-deposited at the muzzle end when the rapidly expanding gas is released to the atmosphere.

I haven't heard that one--and would be very interested in how it was proven.

Have owned at least one bore-scope for over 20 years, and have encountered many barrels that didn't copper-foul much at all near the muzzle. Have probably scoped over 1000 barrels.

Have heard about "vaporized" copper particles causing fouling for a few inches in front of the throat, but also have never read any evidence to prove it. I suspect it does happen, due to the typical maximum-pressure peak which occurs just about when the bullet enters the rifling--which also results in the highest temperatures during the bullet's trip down the bore.

I'm sure it's just a theory, but one of it's proponents is a long time custom barrel manufacturer.

I have not noticed much in the way of copper deposits near the muzzles of any of the custom barrels I own until they were nearly shot out, with severe firecracking for the first few inches.

There are many, many factors contributing to fouling that I wouldn’t say it is universally true. A good barrel in .204 Ruger could feasibly foul less than a low-quality .308 Winchester. The bullets matter, too.

But as a general rule of thumb, I see more copper fouling and see it sooner in my varmint rifles. I had one .17 Remington that would only make 30 or so rounds before it was time to be cleaned.

Hand lapped barrels aren't always better. Use the borescope to evaluate your cleaning methods. Shoot the rifle to determine how accurate it is.

I’ve made it this long without fretting over how my bore looks under magnification and more concerned with how my rifle shoots. I know that if I were to buy and use a bore scope I would suddenly be worrying about something that I need not worry about….picking flyshit out of pepper. 😁

This is not meant as a slight to anyone that uses a bore scope, more like me being self deprecating because I know myself. I know that a bore scope can be an invaluable diagnostic tool but I also know that it can be a riddle with no conclusion for guys like me. I honestly can’t ever think of a time where I needed a bore scope or when a bore scope would’ve helped diagnose a problem. Some rifles seemed to foul more than others and some ammunition seemed to foul more than others but they were all accurate. I used to clean my rifles after every outing and then fire 2 or 3 rounds for “fouling” shots. I realized a couple decades ago that I was mostly wasting my time worrying about minutiae. I no longer clean my rifles after every outing. I now wait until accuracy degrades before giving them a thorough cleaning but I do ALWAYS wipe them down with some G96 or whatever I have handy.

One day about 20 years ago I had an older guy bring in a Savage 99 in .300 Savage that looked as if the metal on one side of the rifle had been attacked by worms. The rifle had been put away in a sheepskin case that was wet and the pitting of the rifle and bore was atrocious. I was young, ambitious and curious so I set about trying to revive the old girl. I had a gunsmith buddy advise me and council me throughout the process. After a lot of time and elbow grease I got to the point where “it’s good enough”. I had my buddy show me how to hot blue the metal at his shop so I bead blasted it and reblued it. I wasn’t trying to make it new again I was simply trying to see if something that far gone could be brought into serviceable condition. I cleaned and scrubbed the bore but it still looked awful. I refinished the wood, “recut” the checkering, added a nice new 1” black recoil pad (Kickeze iirc) and reassembled the rifle. After adding one of the new Weaver 3-9x40 scope in a set of Leupold rings and bases it was time to assess how much time I had wasted with this project. I had bore sighted the rifle at my shop so I knew that I’d be not just “on paper” but that Tasco bore sighter was so good that I was almost always damn close to the bullseye. I set the target at 100 yards and sent the first round down range. I was about 3” high but dead on for windage so I proceeded to shoot a 5 shot group that was under an inch. I couldn’t believe it so I shot another group and then another and another. With 2 different types of factory ammo I shot 2 boxes….8 groups of 5 shots with time for the barrel to cool in between groups. That rifle consistently kept all the groups at just under an inch. I was amazed that a barrel that was pitted and ugly could consistently group so good. If anyone was to use their bore scope on that rifle they’d have puked when they saw how rough the bore was but damn if it didn’t shoot like a house on fire. I kept that rifle and a couple targets from different shoots at the shop and showed countless people that how the bore looked wasn’t always how it shot. I eventually sold it to a long time customer and friend that had been trying for a couple years to talk me out of it. I had gotten more mileage from that Savage than I had ever anticipated and I learned more than expected which would likely have never happened if I had a bore scope. 😁

AcesNeights,

I've been using borescopes for around 20 years now, and have written about them considerably in various magazines, and my books. My take is their highest and best use is to evaluate the effectiveness of cleaning products--and other bore-related products such as Dyna Bore-Coat.

Many new bore-scope users think they'll be able to tell how well a certain barrel will shoot by looking inside the bore, but there are too many factors other than a shiny bore that ultimately affect accuracy. Plus, as many people have noted, even some bores that look bad will shoot very well! In fact, the first article I ever read on borescopes (which appeared maybe 40 yards ago) mentioned this--especially the author's disappointment in the appearance of the bore on of of his favorite and most accurate rifles!

But another good use of a scope, as I've also mentioned in various publications, is being able to monitor the throat area when using bore-lapping bullets to smooth 'em out after heat-erosion starts affecting accuracy. Have done this with several barrels, which extended barrel accuracy-life considerably at relatively little cost. It REALLY helps to be able to tell exactly when the process smooths out the "gator-skin" of erosion--and not shoot too few or too many lapping bullets.

I also found it very interesting, after visiting several barrel-making factories, that some of the best use bore-scopes to evaluate their work, while others totally ignore the possibility. Visited the Lilja factory for the first time over 20 years ago, and Dan had a bore-scope hooked up to a TV-sized screen. In fact, that was one of several factors which convinced me to buy my first scope--which was far more expensive than many of the scopes available today.

John, great post. I noticed that in my hunting rifles that are factory, most will perform their most accurate loads in the first 30-40 shots after cleaning, then they will level off to a plateau of larger group size over a large number of shots.

Now, cleaning a Magnum rifle with 150 rounds on it is a serious labor of love.

All of this is a hobby, but when I keep the copper out of my Remington factory barrels, bedded, freefloated, these factory rifles shoot tuned loads 3/8"-1/2" with boring regularity.

I use Montana Extreme Copper killer, and the Montana Extreme Copper cream on patches and a STIFF plastic brush in the worst cases of carbon and copper. Iosso and Montana Extreme plastic brushes are the best, but regular use of High Quality Bronze bristle brushes carry the heavy lifting in gun cleaning, throw them away with 60-100 strokes on them. After 100 strokes, I save them to scrub really nasty barrels with the Montana Extreme Copper cream, Flitz Rifle Bore cleaner, Flitz, or JB.

I shoot a lot, 308's to 7 mags.

Thanks, Keith.

I pretty much use the same cleaning stuff, but also apply Dyna Bore-Coat to barrels that are particularly prone to copper-fouling, especially my prairie-dog rifles. Have found DBC at least doubles the number of rounds that can be fired before accuracy degrades and bores have to be cleaned, and some rifles can be shot several hundred rounds without cleaning.