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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Why does Barrel fowling spoil accuracy
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<blockquote data-quote="Kevin Thomas" data-source="post: 663924" data-attributes="member: 15748"><p>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.</p><p> </p><p>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. </p><p> </p><p>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. </p><p> </p><p>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. </p><p> </p><p>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.</p></blockquote><p></p>
[QUOTE="Kevin Thomas, post: 663924, member: 15748"] 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. [/QUOTE]
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Why does Barrel fowling spoil accuracy
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