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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="Bart B" data-source="post: 672496" data-attributes="member: 5302"><p>I agree with Kevin's comments on barrel fouling vs accuracy. Kevin's predecessor at Sierra Bullets often "sang the same song" about fouling. And my experience across several 30 caliber barrels has been the same.</p><p></p><p>Comments in this thread about fouling changing a bullet's balance are easy to figure out. </p><p></p><p>If there's a copper wash building up in barrel that started out with bare metal in the bore and groove surfaces, that copper had to come from the bullets. There's no copper in the powder that's deposited on the bore surfaces. As the bullet's lost some of its jacket material, it makes sense to me that it's not uniformly removed around the bullet. The bore surfaces are rougher in some areas than others. As more copper's rubbed off the bullets and imbedded into the micro pits and valleys, the "landscape" smooths up. Eventually little or no copper's removed from subsequent bullets and they remain well balanced as the leave the muzzle. All of which is why it takes a few to several shots to get a rough bore smoothed up to where all the bullets arrive at the same place downrange. But they're not quite as accurate as bullets fired from barrels that have the least copper fouling isues.</p><p></p><p>Hardened powder fouling typically doesn't remove jacket material from a bullet, but it can microscopically change a bullet's shape. A barrel maker told me that it sort of swages down the bullet diameter unevenly around it. Smoother surfaces on the lands and grooves tend to powder foul the least. Powder fouling and residue from a previous shot's drug out with the bullet and carried down range. Bullet holes in target paper wouldn't have dark grey colored edges if there was no powder fouling on the bullet that got rubbed off of it as it passed through the paper. And smooth barrels typically don't get built up layers of powder fouling; it stays constant for dozens of rounds.</p><p></p><p>Best example of how little powder and copper fouling really effect accuracy is the precision test barrels used at Lake City Army Ammunition Plant testing 30 caliber bullets in match ammo. The ballisticians will start out with a squeaky clean barrel aimed at the 600-yard target. Then shoot a couple hundred rounds 30 seconds to a minute apart. Good lots of National Match ammo will have all their bullet holes inside 6 inches. Having seen a couple of those targets, they are impressive for what mass produced ammo from high speed machines will make. And that a good barrel will shoot a bunch of rounds very accurate without cleaning.</p><p></p><p>In another test with a Hart barrel in .308 Win., a dozen or so 10-shot groups with Lapua 185-gr. FMJRB match bullets all go under 1.5 inches at 600 yards. Then a 40-shot group had all bullets under 2 inches. Barrel wasn't cleaned for those 160 or so shots.</p><p></p><p>It's my opinion that while copper and powder fouling will happen, if its minimal and consistant throughout the bore, excellent accuracy will happen for many, many shots. Bullets fired through fouled barrels that ain't unbalanced will shoot very accurate.</p></blockquote><p></p>
[QUOTE="Bart B, post: 672496, member: 5302"] I agree with Kevin's comments on barrel fouling vs accuracy. Kevin's predecessor at Sierra Bullets often "sang the same song" about fouling. And my experience across several 30 caliber barrels has been the same. Comments in this thread about fouling changing a bullet's balance are easy to figure out. If there's a copper wash building up in barrel that started out with bare metal in the bore and groove surfaces, that copper had to come from the bullets. There's no copper in the powder that's deposited on the bore surfaces. As the bullet's lost some of its jacket material, it makes sense to me that it's not uniformly removed around the bullet. The bore surfaces are rougher in some areas than others. As more copper's rubbed off the bullets and imbedded into the micro pits and valleys, the "landscape" smooths up. Eventually little or no copper's removed from subsequent bullets and they remain well balanced as the leave the muzzle. All of which is why it takes a few to several shots to get a rough bore smoothed up to where all the bullets arrive at the same place downrange. But they're not quite as accurate as bullets fired from barrels that have the least copper fouling isues. Hardened powder fouling typically doesn't remove jacket material from a bullet, but it can microscopically change a bullet's shape. A barrel maker told me that it sort of swages down the bullet diameter unevenly around it. Smoother surfaces on the lands and grooves tend to powder foul the least. Powder fouling and residue from a previous shot's drug out with the bullet and carried down range. Bullet holes in target paper wouldn't have dark grey colored edges if there was no powder fouling on the bullet that got rubbed off of it as it passed through the paper. And smooth barrels typically don't get built up layers of powder fouling; it stays constant for dozens of rounds. Best example of how little powder and copper fouling really effect accuracy is the precision test barrels used at Lake City Army Ammunition Plant testing 30 caliber bullets in match ammo. The ballisticians will start out with a squeaky clean barrel aimed at the 600-yard target. Then shoot a couple hundred rounds 30 seconds to a minute apart. Good lots of National Match ammo will have all their bullet holes inside 6 inches. Having seen a couple of those targets, they are impressive for what mass produced ammo from high speed machines will make. And that a good barrel will shoot a bunch of rounds very accurate without cleaning. In another test with a Hart barrel in .308 Win., a dozen or so 10-shot groups with Lapua 185-gr. FMJRB match bullets all go under 1.5 inches at 600 yards. Then a 40-shot group had all bullets under 2 inches. Barrel wasn't cleaned for those 160 or so shots. It's my opinion that while copper and powder fouling will happen, if its minimal and consistant throughout the bore, excellent accuracy will happen for many, many shots. Bullets fired through fouled barrels that ain't unbalanced will shoot very accurate. [/QUOTE]
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Why does Barrel fowling spoil accuracy
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