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280 AI alert
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<blockquote data-quote="Pdvdh" data-source="post: 2102017" data-attributes="member: 4191"><p>I revive a 10-year old Thread. Because as recently as yesterday, the decade long debate and disagreement as to whether there is a difference in headspace between PO Ackley's traditional 280 AI, and Nosler's SAAMI adopted "280 Ackley Improved" cartridge continued, in a separate Thread on the Forum.</p><p></p><p>The answer is: <u><strong>The traditional <u>280 AI</u> chamber headspace is 0.0142" longer (deeper) than Nosler's SAAMI "280 Ackley Improved".</strong></u> Below is the indisputable mathematical solution, and proof. The only level of math required is subtraction.</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 PO Ackley'straditional 280 AI.</p><p></p><p>[ATTACH=full]247736[/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]247740[/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" shorter 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 'Ackley improved' chamber. This technique forces the parent case to instead, stretch in the shoulder area to fill the larger 'improved' chamber ID.</p><p></p><p>Let's begin the math - simple subtraction:</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 Ackley's 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><span style="font-size: 22px">"</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 their shoulders.</p><p></p><p>It should come as no surprise that J E Custom had it nailed down correctly from the very get-go.</p></blockquote><p></p>
[QUOTE="Pdvdh, post: 2102017, member: 4191"] I revive a 10-year old Thread. Because as recently as yesterday, the decade long debate and disagreement as to whether there is a difference in headspace between PO Ackley's traditional 280 AI, and Nosler's SAAMI adopted "280 Ackley Improved" cartridge continued, in a separate Thread on the Forum. The answer is: [U][B]The traditional [U]280 AI[/U] chamber headspace is 0.0142" longer (deeper) than Nosler's SAAMI "280 Ackley Improved".[/B][/U] Below is the indisputable mathematical solution, and proof. The only level of math required is subtraction. 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 PO Ackley'straditional 280 AI. [ATTACH type="full" alt="SAAMI 280 Remington (7mm Express Remington) Chamber Dimensions.JPG"]247736[/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"]247740[/ATTACH] P.O. Ackley's standard practice when improving a parent cartridge was to set the chamber neck/shoulder junction back 0.004" shorter 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 'Ackley improved' chamber. This technique forces the parent case to instead, stretch in the shoulder area to fill the larger 'improved' chamber ID. Let's begin the math - simple subtraction: "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 Ackley's 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][SIZE=6]"[/SIZE][/B] Since both cartridges share the same 40-degree shoulder angle, the 0.0142" difference is maintained at any common datum point along their shoulders. It should come as no surprise that J E Custom had it nailed down correctly from the very get-go. [/QUOTE]
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