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Why does Barrel fowling spoil accuracy

 
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  #8  
Old 06-18-2012, 06:19 AM
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Re: Why does Barrel fowling spoil accuracy

I don't believe that high shot count repeatability is caliber dependent. Barrel, load, bullet, etc all play a role in how long you can maintain tight groups without having to clean the barrel. I have two 6.5x284's. My Cooper will maintain it's accuracy clean, dirty, hot, or cold for at least 50 rounds. The Savage needs a few foulers, but will then hold for around 30 or 40 shots. The Savage bore is pretty rough. I wouln't have expected it. They could go longer, but I haven't tried. The Savage shoots better withH4831sc, the Cooper with Retumbo. Also, I had two identicle Remington 308 Milspec's for competition. One would shoot over 200 rounds holding accuracy, the other only 30 or 40 rounds, both with the same load. I have shot lots of other rifles over the years of different calibers but no patterns specific to caliber as far as number of accurate rounds can be achieved before cleaning.
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Old 06-18-2012, 09:18 AM
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Re: Why does Barrel fowling spoil accuracy

Good stuff guys very interesting !
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  #10  
Old 06-18-2012, 09:42 AM
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Re: Why does Barrel fowling spoil accuracy

Number one, very few people have ever bothered to actually check the accuracy of a given barrel as fouling develops, much less doing so in a scientifically valid manner. We tend to take for granted the "fact" that groups will open up, or go completely to hell if a barrel isn't cleaned completely after, 20, 30, 40, or however many rounds. That's not necessarily the case. To begin with, fouling only goes so far; it's not like your 308 will keep fouling until it becomes a 7-08. They can fire one helluva lot more rounds than most will believe, simply because we hear this stuff repeated so often.

Some years back I was tasked with testing a wide variety of various moly coatings (and similar products) to select the best. As a baseline, since everyone was so committed to the idea that these coatings would allow the shooter to fire so many more rounds without cleaning than uncoated rounds would, I wanted to find out what happens when we run this many rounds of uncoated bullets without cleaning. 300 was a magic number that I kept hearing from the guys who were committed to moly, so that's what I used. I loaded and fired a total of 300 rounds of uncoated 168s in a 308 Win, from a machine rest, in a series of 10 round groups. Simultaneously, each series of 10-rounds groups went into a fifty round composite. All firing was done at 200 yards, in a tunnel, and without ever moving the test barrel from the machine rest. The gun was a 308 Winchester (Obermeyer reamer), using a 1x12" Hart (as I recall) buttoned barrel. When I was done, I had a series of thirty (30) ten-round groups, and six (6) fifty round groups to evaluate. The point here was to see at what point the accuracy dropped off to a measurable (and statistically significant) point. After all the firing, there was virtually no noticable degradation of group size throughout the test. The 50 round composite groups were where things got interesting. In them, they became slightly tighter throughout the test, with the single smallest fifty round group being the last one, shots #251 through 300.

Bottom line here is, most shooters worry way too much about this, and don't really know just how long a good barrel will hold its accuracy.

Barrels are different, and certainly a crappy barrel will often show more fouling than a better made sample. We're talking about differences in the barrel itself here, not the fouling per se. Which is why I have a very simple policy regarding such things; Life's too short to waste time with bad barrels. Use decent quality barrels, and things are just so much easier.

Different calibers (naturally) will show different tendencies here as well, and that has to be accounted and adjusted for. Know that going in, and let that be a factor in selecting your next chambering, if that's an issue for you.
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  #11  
Old 06-18-2012, 12:44 PM
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Re: Why does Barrel fowling spoil accuracy

^ Bang on.

A sub-premium barrel typically has more machine and tooling marks throughout the bore, and these imperfections in the steel like to scrape off, and gather copper from passing bullets. As these areas of barrel imperfections accumulate copper, they tend to damage and slightly de-balance each passing bullet. There are products on the market that cure as a hard ceramic coating, and are designed to fill in these little divots and areas of imperfection in the bore. These coatings cure at a couple of microns thickness in the "normal" portions of the bore, so they effectively leave a smooth surface throughout the length of the bore, which makes it much harder for copper to be stripped from the bullet jacket and accumulate in the bore.

A premium barrel with no visible tooling marks would behave in like manner.
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Old 06-18-2012, 05:18 PM
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Re: Why does Barrel fowling spoil accuracy

I won't accept any baloney about 'over-worrying' about my fouling. It is pretty obvious when MY barrels are done for the day, and only cleaning will recover performance. It's like a damn switch is flipped.

While it's interesting that there are barrels that defy copper fouling, it really doesn't apply with all the others. A 'scientific' test would include a barrel that DOES copper foul out. Right?
Did you test any of them Kevin?
Most of us have seen or had em, they're not unicorn barrels or anything..
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  #13  
Old 06-19-2012, 02:35 PM
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Re: Why does Barrel fowling spoil accuracy

In addition to other phenomenon cited, I didn't catch where anybody here mentioned bearing surface and twist.

Litz mentioned in another thread regarding the upcoming 7mm 195gr Berger that the extreme length (bearing surface) may lead to excessive fouling for target rifles with long shot strings.

One of the guys at Bartlein also told me that one of the drawbacks of progressive (gain) twist is that there's continuous morphing of the jacket as the rate of twist increases which seems to lead to more fouling.

I do agree with Kevin that not enough attention is paid to proving these things statistically through scientific method. But like MikeCR points out, the study could've benefitted from one or more barrels known/alleged to be negatively impacted by fouling. And, I'd suggest perhaps that some should be included that are known/alleged to be positively affected by fouling.

The great thing about a well thought out experiement is that it should be repeatable.

Good discussion. But, how cool would it be to get paid to research this stuff!

-- richard
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  #14  
Old 06-19-2012, 07:31 PM
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Re: Why does Barrel fowling spoil accuracy

Mike, if you'd be so kind, please point out where I said that the barrels didn't foul? They did. But it didn't degrade the accuracy like I expected it to, which was a fair bit of a surprise to me. I routinely cleaned every 40-50 shots, simply because I'd always done it that way, and that was the routine I'd gotten into. Over the years, that became more or less standard protocol, simply by repitition. The point to doing this series was the fact that I'd never let one go that far, and wanted to see what happened. I'm not alone here, either. My friend Derrick Martin once shot an entire season without cleaning his bore, just to see what happened. End result? Absolutely nothing. He shot the same High Master scores (an average of 97% or above) throughout the season, just like when he regularly cleaned the rifle. I seem to recall that the late Warren Page onve did the same thing with one of his BenchRest rifles, and found much the same thing. I think there's some historical reasons for why these claims were originally made (and they WERE valid at that time) but have simply been parrotted by gunwriters and shooteers ever since, even though it's no longer nearly as critical now as it once was. Sorry to slaughter the sacred cow here, but there it is.

I shot an average of 400-600 rounds a day, normally six days a week, for over twenty years. Cleaning every 40-50 rounds (as I did), that's a bunch of cleaning. All barrels are slightly different, but they are usually fairly similar in how they behave. I cited a specific example, naming both the barrel make, chambering and twist that I ran the test with. Given a larger cased cartridge, the results may have been a bit different. I recall that when the 7mm STW first hit the scene, there was at least one guy who chambered one up as a 1,000 yard prone gun. Didn't work, due (in his opinion) to fouling issues. You need a cartridge/barrel combination that will go at least 20+ rounds for that game, and his rifle wouldn't do it. Started off fine, but accuracy degraded horribly by the time he got into his second string. Could have been powder foulng, could have been metal fouling, who knows. But it didn't work. Point is, the combinations are different, and need to be handled on an individual basis. You clean all you want, but I'm content to let the barrel tell me when it needs it . . . and don't be surprised if you don't hear from it for a while.

As far as sacred cows go, I like mine rare, and sitting beside a loaded baked potato.
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