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Rifles, Reloading, Optics, Equipment
Reloading
Case neck thickness measurements
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<blockquote data-quote="Bart B" data-source="post: 678163" data-attributes="member: 5302"><p>Yes, "15" on the dial indicator means .015 inch; or .38 mm in the metric system.</p><p></p><p>From Redding's web site for that gauge: </p><p></p><p>(<a href="http://www.redding-reloading.com/online-catalog/46-case-neck-gauge" target="_blank">Case Neck Gauge | Redding Reloading Equipment: reloading equipment for rifles, handguns, pistols, revolvers and SAECO bullet casting equipment</a>)</p><p></p><p>That information's somewhat misleading. It's been my experience that 30 caliber case neck thickness can vary as much as .002 inch (.050 mm) and excellent accuracy can be had. Even with standard chamber neck diameters allowing .003 to .004 inch clearance around the case neck. Those "tight neck" chambers referred to on Redding's web site are used by folks who think best accuracy happens when necks are tight and only .001 inch or so of clearance helps center the case neck and also the bullet more precicely in the chamber. They typically don't realize nor understand that bottleneck cases headspacing on their shoulder center perfectly in the chamber neck wnen the firing pin drives the case shoulder hard into the chamber's matching shoulder centering the case perfectly there and therefore centering the bullet very well in the bore. </p><p></p><p>It's also interesting that folks in the USA getting the best accuracy from the .308 Win. case do so with full length sizing dies using a neck bushing whose diameter's 2 to 3 thousandths inch smaller than a loaded round's neck diameter. No expander ball's used as they tend to bend case necks as the come up through the case neck.</p><p></p><p>Those Lapua cases have a range of .0145 inch to .019 inch neck wall thickness. That's quite a bit. If best accuracy is desired, I'd get a neck turning tool and turn all the neck down to .0155 inch maximum. That'll clean up most of them and the .001 inch spread in those few that don't clean up all the way around won't matter. Case neck tension on the bullets will be a lot more uniform and that'll help keep muzzle velocity spread at reasonable levels.</p><p></p><p>I've shot fullbore matches at the General DeWet rifle range near Bloomfontein using SA arsenal 7.62 NATO ammunition loaded with Sierra 155 match bullets in cases with a .002 inch spread in neck wall thickness. That's very good for mass produced cases and that ammo shot about as good as handloaded stuff does in the USA. And folks shooting fullbore matches around the world don't use "tight neck" chambers; they pretty much all standard size. If you know anyone in SA who shoots fullbore, ask them about neck wall thickness and other stuff that makes the .308 a favorite for long range competition around the world.</p></blockquote><p></p>
[QUOTE="Bart B, post: 678163, member: 5302"] Yes, "15" on the dial indicator means .015 inch; or .38 mm in the metric system. From Redding's web site for that gauge: ([url=http://www.redding-reloading.com/online-catalog/46-case-neck-gauge]Case Neck Gauge | Redding Reloading Equipment: reloading equipment for rifles, handguns, pistols, revolvers and SAECO bullet casting equipment[/url]) That information's somewhat misleading. It's been my experience that 30 caliber case neck thickness can vary as much as .002 inch (.050 mm) and excellent accuracy can be had. Even with standard chamber neck diameters allowing .003 to .004 inch clearance around the case neck. Those "tight neck" chambers referred to on Redding's web site are used by folks who think best accuracy happens when necks are tight and only .001 inch or so of clearance helps center the case neck and also the bullet more precicely in the chamber. They typically don't realize nor understand that bottleneck cases headspacing on their shoulder center perfectly in the chamber neck wnen the firing pin drives the case shoulder hard into the chamber's matching shoulder centering the case perfectly there and therefore centering the bullet very well in the bore. It's also interesting that folks in the USA getting the best accuracy from the .308 Win. case do so with full length sizing dies using a neck bushing whose diameter's 2 to 3 thousandths inch smaller than a loaded round's neck diameter. No expander ball's used as they tend to bend case necks as the come up through the case neck. Those Lapua cases have a range of .0145 inch to .019 inch neck wall thickness. That's quite a bit. If best accuracy is desired, I'd get a neck turning tool and turn all the neck down to .0155 inch maximum. That'll clean up most of them and the .001 inch spread in those few that don't clean up all the way around won't matter. Case neck tension on the bullets will be a lot more uniform and that'll help keep muzzle velocity spread at reasonable levels. I've shot fullbore matches at the General DeWet rifle range near Bloomfontein using SA arsenal 7.62 NATO ammunition loaded with Sierra 155 match bullets in cases with a .002 inch spread in neck wall thickness. That's very good for mass produced cases and that ammo shot about as good as handloaded stuff does in the USA. And folks shooting fullbore matches around the world don't use "tight neck" chambers; they pretty much all standard size. If you know anyone in SA who shoots fullbore, ask them about neck wall thickness and other stuff that makes the .308 a favorite for long range competition around the world. [/QUOTE]
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