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Rifles, Reloading, Optics, Equipment
Reloading
RCBS Precision Mic
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<blockquote data-quote="Kevin Thomas" data-source="post: 368797" data-attributes="member: 15748"><p>Tom,</p><p> </p><p>sorry for the confusion here, but it IS a complex topic. The dimension we're taking into account here is the actual "play" or space between the shoulder of a chambered round, and the internal angle of the chamber. Or, if you prefer, the space between the head of a chambered round and the face of the closed bolt. In otherwords, the headspace. This reference is used to describe the portion of a firearm's chamber, or, a cartridge, that prevents it from entering any deeper. This can be the rim on a rimmed case (44 Magnum, 30-30 WCF, 38 Spl, etc.), the belt on a magnum (458 Win Mag, 375 H&H, etc.) or the case mouth on a straight walled rimless case (45 ACP, 9mm or 40 S&W, etc.). It has to coincide with some mechanical point of the firearm that it engages and stops that forward movement. In the case of a rimless, bottlenecked case like we've been discussing here, that point is where the shoulder angle of the cartridge case contacts the shoulder angle of the chamber. The distance between the head of the case (in any of the different styles of cartridges I've mentioned so far) and the pont that stops forward movement is called headspace and refers to the distance to the datum line. This isn't the number to worry about, and it's more the concern of a gunsmith, not the reloader. The headspace dimensions, that .001" to .003" or so of slop that allows the cartridges to chamber and fire properly, are what we need to consider. Not enough space and you have tight chambering issues and <u>will</u> eventually run into a situation where the rounds <u>won't</u> chamber. Too much, and you've got brass that fails very quickly, potentially hazardous case head separations, accuracy problems and misfires. Pays to get it right, and the case gage is the best way to do this. Once you've had a chancve to use these tools just a bit, this stuff will all become second nature to you, and you'll have a very clear understanding of what's going on. It's just new to you right now, and we've all been there. </p><p> </p><p>Kevin Thomas</p><p>Lapua USA</p></blockquote><p></p>
[QUOTE="Kevin Thomas, post: 368797, member: 15748"] Tom, sorry for the confusion here, but it IS a complex topic. The dimension we're taking into account here is the actual "play" or space between the shoulder of a chambered round, and the internal angle of the chamber. Or, if you prefer, the space between the head of a chambered round and the face of the closed bolt. In otherwords, the headspace. This reference is used to describe the portion of a firearm's chamber, or, a cartridge, that prevents it from entering any deeper. This can be the rim on a rimmed case (44 Magnum, 30-30 WCF, 38 Spl, etc.), the belt on a magnum (458 Win Mag, 375 H&H, etc.) or the case mouth on a straight walled rimless case (45 ACP, 9mm or 40 S&W, etc.). It has to coincide with some mechanical point of the firearm that it engages and stops that forward movement. In the case of a rimless, bottlenecked case like we've been discussing here, that point is where the shoulder angle of the cartridge case contacts the shoulder angle of the chamber. The distance between the head of the case (in any of the different styles of cartridges I've mentioned so far) and the pont that stops forward movement is called headspace and refers to the distance to the datum line. This isn't the number to worry about, and it's more the concern of a gunsmith, not the reloader. The headspace dimensions, that .001" to .003" or so of slop that allows the cartridges to chamber and fire properly, are what we need to consider. Not enough space and you have tight chambering issues and [U]will[/U] eventually run into a situation where the rounds [U]won't[/U] chamber. Too much, and you've got brass that fails very quickly, potentially hazardous case head separations, accuracy problems and misfires. Pays to get it right, and the case gage is the best way to do this. Once you've had a chancve to use these tools just a bit, this stuff will all become second nature to you, and you'll have a very clear understanding of what's going on. It's just new to you right now, and we've all been there. Kevin Thomas Lapua USA [/QUOTE]
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