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Rifles, Reloading, Optics, Equipment
Gunsmithing
280 Ackley Chamber
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<blockquote data-quote="Pdvdh" data-source="post: 2101454" data-attributes="member: 4191"><p><strong>I present the final chapter of this decade long saga. </strong>Solved by a simple engineer. A lowly mathematician. A guy that's never operated a metal machine lathe. Mr. Kiff, should he read this, will remember me from the conflict of days gone by on the Shooters' Forum. Even though that embarassing thread was deleted shortly after I confounded that Forum's experts.</p><p></p><p><u>Some background</u>: I went thru laborious trigonometric calculations years back in order to mathematically demonstrate that P.O. Ackley's traditional 280 AI would indeed have a headspace measured from its case head to the 0.375" diameter datum on its 40-degree shoulder that is 0.014" longer than the headspace on Nosler's SAAMI adopted "280 Ackley Approved". In order to complete the math, I was forced to educate myself on the ways, means, methods, and standardized practices of P.O. Ackley's improved cartridges.</p><p></p><p>This Thread caused me to re-evaluate and search for a reliable and simpler way to settle the continuing difference of positions. In a way most could follow and solve using nothing more than mathematical subtraction. Between my prior exercise in trigonometry and schooling on the P.O. Ackley's standard operating procedure for 'improving' parent cartridges, the light bulb came to life.</p><p></p><p>Below is the SAAMI "280 Remington (7mm Express Remington)" chamber drawing. Look at the drawing and find the Breech Bolt Face to neck/shoulder junction distance of 2.1924". This is the parent cartridge of the PO Ackley improved.</p><p></p><p>[ATTACH=full]247551[/ATTACH]</p><p></p><p>Here's the Nosler version, the SAAMI "280 Ackley Improved" chamber drawing. Look at the drawing and find the Breech Face to neck/shoulder junction distance of 2.1742".</p><p></p><p>[ATTACH=full]247556[/ATTACH]</p><p></p><p>P.O. Ackley's standard practice when improving a parent cartridge was to set the chamber neck/shoulder junction back 0.004" less than that of the parent cartridge. This ensured the bolt would close on the parent cartridge case with a 0.004" crush fit. This crush fit holds the parent cartridge case head in firm contact with the bolt face, so the case web doesn't stretch during the initial fire forming of the parent cartridge in the 'Improved' chamber. This technique forces the parent case to instead, stretch in the shoulder area to fill the larger 'improved' chamber ID. 25WSM is in agreement. He stated this is what PO Ackley said to do in post #54.</p><p></p><p></p><p><u>Here's 'the rest of the story'. The <strong>FINAL</strong> conclusion:</u></p><p>"280 Remington" breech bolt face to neck/shoulder junction distance from SAAMI = 2.1924". Reduce this distance by 0.004" in conformance with PO Ackley's standard practice, for Ackley improving the 280 Remington.</p><p>2.1924" - 0.004" = <strong>2.1884"</strong> This is the breech bolt face distance to case neck/shoulder junction for the Ackley improved 280 cartridge. Also commonly known as the traditional 280 AI.</p><p></p><p>"280 Ackley Improved" breech face to neck/shoulder junction distance from SAAMI = <strong>2.1742"</strong>.</p><p></p><p>Subtract the smaller/shorter <u>"280 Ackley Improved" </u><strong><u>2.1742"</u></strong> distance from the from the larger/longer <strong><u>2.1884"</u></strong><u> for the traditional 280 AI</u>.</p><p></p><p><strong>2.1884" minus 2.1742" equals <span style="font-size: 18px">0.0142"</span></strong></p><p></p><p>Since both cartridges share the same 40-degree shoulder angle, the 0.0142" difference is maintained at any common datum point along the shoulder.</p><p></p><p><span style="font-size: 15px">I <em>really</em> hate being right! And it should come as no surprise that J E Custom had it nailed down, right from the very get-go.</span></p></blockquote><p></p>
[QUOTE="Pdvdh, post: 2101454, member: 4191"] [B]I present the final chapter of this decade long saga. [/B]Solved by a simple engineer. A lowly mathematician. A guy that's never operated a metal machine lathe. Mr. Kiff, should he read this, will remember me from the conflict of days gone by on the Shooters' Forum. Even though that embarassing thread was deleted shortly after I confounded that Forum's experts. [U]Some background[/U]: I went thru laborious trigonometric calculations years back in order to mathematically demonstrate that P.O. Ackley's traditional 280 AI would indeed have a headspace measured from its case head to the 0.375" diameter datum on its 40-degree shoulder that is 0.014" longer than the headspace on Nosler's SAAMI adopted "280 Ackley Approved". In order to complete the math, I was forced to educate myself on the ways, means, methods, and standardized practices of P.O. Ackley's improved cartridges. This Thread caused me to re-evaluate and search for a reliable and simpler way to settle the continuing difference of positions. In a way most could follow and solve using nothing more than mathematical subtraction. Between my prior exercise in trigonometry and schooling on the P.O. Ackley's standard operating procedure for 'improving' parent cartridges, the light bulb came to life. Below is the SAAMI "280 Remington (7mm Express Remington)" chamber drawing. Look at the drawing and find the Breech Bolt Face to neck/shoulder junction distance of 2.1924". This is the parent cartridge of the PO Ackley improved. [ATTACH type="full" alt="SAAMI 280 Remington (7mm Express Remington) Chamber Dimensions.JPG"]247551[/ATTACH] Here's the Nosler version, the SAAMI "280 Ackley Improved" chamber drawing. Look at the drawing and find the Breech Face to neck/shoulder junction distance of 2.1742". [ATTACH type="full" alt="SAAMI 280 Ackley Improved Chamber Dimensions.JPG"]247556[/ATTACH] P.O. Ackley's standard practice when improving a parent cartridge was to set the chamber neck/shoulder junction back 0.004" less than that of the parent cartridge. This ensured the bolt would close on the parent cartridge case with a 0.004" crush fit. This crush fit holds the parent cartridge case head in firm contact with the bolt face, so the case web doesn't stretch during the initial fire forming of the parent cartridge in the 'Improved' chamber. This technique forces the parent case to instead, stretch in the shoulder area to fill the larger 'improved' chamber ID. 25WSM is in agreement. He stated this is what PO Ackley said to do in post #54. [U]Here's 'the rest of the story'. The [B]FINAL[/B] conclusion:[/U] "280 Remington" breech bolt face to neck/shoulder junction distance from SAAMI = 2.1924". Reduce this distance by 0.004" in conformance with PO Ackley's standard practice, for Ackley improving the 280 Remington. 2.1924" - 0.004" = [B]2.1884"[/B] This is the breech bolt face distance to case neck/shoulder junction for the Ackley improved 280 cartridge. Also commonly known as the traditional 280 AI. "280 Ackley Improved" breech face to neck/shoulder junction distance from SAAMI = [B]2.1742"[/B]. Subtract the smaller/shorter [U]"280 Ackley Improved" [/U][B][U]2.1742"[/U][/B] distance from the from the larger/longer [B][U]2.1884"[/U][/B][U] for the traditional 280 AI[/U]. [B]2.1884" minus 2.1742" equals [SIZE=5]0.0142"[/SIZE][/B] Since both cartridges share the same 40-degree shoulder angle, the 0.0142" difference is maintained at any common datum point along the shoulder. [SIZE=4]I [I]really[/I] hate being right! And it should come as no surprise that J E Custom had it nailed down, right from the very get-go.[/SIZE] [/QUOTE]
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