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Rifles, Reloading, Optics, Equipment
Reloading
Measuring to the lands
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<blockquote data-quote="Bart B" data-source="post: 1123259" data-attributes="member: 5302"><p>Bob4, if you're handholding your rifle against your shoulder as it rests on something atop a bench, I think the real accuracy of it with that ammo is much better than your groups show. Us humans tend to degrade a rifle and ammo's accuracy quite a bit. We don't hold the rifle exactly the same like a machine rest does. Nor as repeatable as one fired in free recoil. It's my experience observing people shooting their stuff from the traditional (not benchrest match free recoil type) position holding on to it shoot much smaller test groups slung up in prone such as what's now used in F-class matches. Same with my own tests.</p><p></p><p>Anyone believing one few-shot group represents what the size of several with that load will be should review the following results from the 2015 NBRSA Nationals:</p><p></p><p><a href="http://www.benchrest.com/showthread.php?93618-2015-NBRSA-Nationals-Complete-Results" target="_blank">2015 NBRSA Nationals Complete Results</a></p><p></p><p>Check out any given competitors smallest and largest groups fired for aggregate scores; specifically the match winners. Note how much bigger the largest one is compared to the smallest one. No competitor's groups in any aggregate match (average size of all groups fired) are within 10% of the same size. And sometimes, the smallest group fired is not part of any winning aggregate. There's a spread of two times to several times larger from the smallest group shot to the largest. Rarely is the first group shot the smallest of all of them.</p><p></p><p>If anyone can shoot their stuff in groups of any size that all have no more than a 10% spread across them, I applaud them. I've yet to see any proof of that.</p><p></p><p>Regarding bullet jump distance to the rifling. I've measured throat advancement across several .308 Win and 30-.338 Win Mag barrels and one .264 Win Mag barrel over their accurate life. "Life" is when average accuracy test fired group sizes get about 50% bigger than when the barrels were new. That's Sierra Bullets' standard for their test barrels used to measure their stuff's accuracy to meet their specs. Here's the average numbers for throat advancement in my barrels:</p><p></p><p>Seventeen or so .308's: .001" advancement for every 40 shots. Total after about 3000 rounds, .075". MIL SPEC throat erosion gauges in the barrels used in Garands went in about 1/3rd inch further at that round count than when new. They're tapered at .010" diameter per inch of length of the gauging head. Gauges went in about 1/10th inch further in for every 1000 rounds fired.</p><p></p><p>Four 30-.338's: .001" advancement for every 15 shots. Total after about 1300 rounds, .085".</p><p></p><p>One .264: .001" advancement for every 7 shots. Total after about 640 rounds, .095".</p><p></p><p>.</p></blockquote><p></p>
[QUOTE="Bart B, post: 1123259, member: 5302"] Bob4, if you're handholding your rifle against your shoulder as it rests on something atop a bench, I think the real accuracy of it with that ammo is much better than your groups show. Us humans tend to degrade a rifle and ammo's accuracy quite a bit. We don't hold the rifle exactly the same like a machine rest does. Nor as repeatable as one fired in free recoil. It's my experience observing people shooting their stuff from the traditional (not benchrest match free recoil type) position holding on to it shoot much smaller test groups slung up in prone such as what's now used in F-class matches. Same with my own tests. Anyone believing one few-shot group represents what the size of several with that load will be should review the following results from the 2015 NBRSA Nationals: [url=http://www.benchrest.com/showthread.php?93618-2015-NBRSA-Nationals-Complete-Results]2015 NBRSA Nationals Complete Results[/url] Check out any given competitors smallest and largest groups fired for aggregate scores; specifically the match winners. Note how much bigger the largest one is compared to the smallest one. No competitor’s groups in any aggregate match (average size of all groups fired) are within 10% of the same size. And sometimes, the smallest group fired is not part of any winning aggregate. There's a spread of two times to several times larger from the smallest group shot to the largest. Rarely is the first group shot the smallest of all of them. If anyone can shoot their stuff in groups of any size that all have no more than a 10% spread across them, I applaud them. I’ve yet to see any proof of that. Regarding bullet jump distance to the rifling. I’ve measured throat advancement across several .308 Win and 30-.338 Win Mag barrels and one .264 Win Mag barrel over their accurate life. “Life” is when average accuracy test fired group sizes get about 50% bigger than when the barrels were new. That’s Sierra Bullets’ standard for their test barrels used to measure their stuff’s accuracy to meet their specs. Here’s the average numbers for throat advancement in my barrels: Seventeen or so .308's: .001" advancement for every 40 shots. Total after about 3000 rounds, .075". MIL SPEC throat erosion gauges in the barrels used in Garands went in about 1/3rd inch further at that round count than when new. They're tapered at .010" diameter per inch of length of the gauging head. Gauges went in about 1/10th inch further in for every 1000 rounds fired. Four 30-.338's: .001" advancement for every 15 shots. Total after about 1300 rounds, .085". One .264: .001" advancement for every 7 shots. Total after about 640 rounds, .095". . [/QUOTE]
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