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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Custom throat?
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<blockquote data-quote="TxAggie94" data-source="post: 1275391" data-attributes="member: 12272"><p>So, whether or not I ultimately decide to ask for a custom length, I do want to make sure I understand. First step is to figure out where the ogive would fall relative to the SAAMI spec chamber if seated for full neck contact.</p><p></p><p>If I look at the SAAMI chamber dimensions, it looks to me like it is nominally 0.491" from the shoulder/neck junction of the chamber to where the lands start....and 0.5626" from the junction to where there would be full engagement. </p><p></p><p>I know I am ignoring tolerances, brass thickness, junction radius and any gap between case shoulder and chamber.</p><p></p><p>Next, I would determine the length of the bearing surface for the chosen bullet and compare that to one of the neck-to-lands measurements above. If the bullet bearing surface is longer, then I have to seat deep or have the rifle throated long. If the bearing surface is shorter, then I have to load long and give up neck contact or have the rifle throated short. </p><p></p><p>Unfortunately, all the uncertainties now come in to play. Which length do I use? The 0.491 to where the freebore first gives way to the lands? or the 0.5626"</p><p></p><p>Further, depending on how you measure or determine bearing surface length of the bullet, the distance from shoulder/neck junction to the bullet ogive for the 3 bullets I am considering are:</p><p> * 195 Berger: 0.524</p><p> * 175 ABLR (posted): 0.623 </p><p> * 175 ABLR (measured): 0.664</p><p> * 175 ELD-X: 0.57</p><p></p><p>Of course, these numebrs are all from different sources, so I can't really do a direct comparison. The Berger value came from Berger.com. The 175 ABLR (posted) and ELD-X values were posted on LRH. The measured ABLR value (0.664) I measured with the hornady gage. I don't know which values to believe for what I am trying to do. If I already had the rifle chambered, I would seat a bullet deep in a fired case, load it, and push it forward (through a drilled-out flash hole) until I feel resistance. Then I know where the lands are. Trying to figure it theoretically leaves me with a lot of doubts.</p><p></p><p>I guess Garycrow is right...the way to do this is simply pick a bullet and seat it as desired and send it in to have the chamber throated to match. </p><p></p><p>I guess the reason I started this exercise is what MudRunner alluded to: if I have it throated specifically for one of the bullets and then that one doesn't shoot for some reason at any length, it may leave me having to load long for one of the others in order to get it to shoot. </p><p>I'm probably overthinking. I just can't afford to do this twice, so I want it right the first time.</p></blockquote><p></p>
[QUOTE="TxAggie94, post: 1275391, member: 12272"] So, whether or not I ultimately decide to ask for a custom length, I do want to make sure I understand. First step is to figure out where the ogive would fall relative to the SAAMI spec chamber if seated for full neck contact. If I look at the SAAMI chamber dimensions, it looks to me like it is nominally 0.491" from the shoulder/neck junction of the chamber to where the lands start....and 0.5626" from the junction to where there would be full engagement. I know I am ignoring tolerances, brass thickness, junction radius and any gap between case shoulder and chamber. Next, I would determine the length of the bearing surface for the chosen bullet and compare that to one of the neck-to-lands measurements above. If the bullet bearing surface is longer, then I have to seat deep or have the rifle throated long. If the bearing surface is shorter, then I have to load long and give up neck contact or have the rifle throated short. Unfortunately, all the uncertainties now come in to play. Which length do I use? The 0.491 to where the freebore first gives way to the lands? or the 0.5626" Further, depending on how you measure or determine bearing surface length of the bullet, the distance from shoulder/neck junction to the bullet ogive for the 3 bullets I am considering are: * 195 Berger: 0.524 * 175 ABLR (posted): 0.623 * 175 ABLR (measured): 0.664 * 175 ELD-X: 0.57 Of course, these numebrs are all from different sources, so I can't really do a direct comparison. The Berger value came from Berger.com. The 175 ABLR (posted) and ELD-X values were posted on LRH. The measured ABLR value (0.664) I measured with the hornady gage. I don't know which values to believe for what I am trying to do. If I already had the rifle chambered, I would seat a bullet deep in a fired case, load it, and push it forward (through a drilled-out flash hole) until I feel resistance. Then I know where the lands are. Trying to figure it theoretically leaves me with a lot of doubts. I guess Garycrow is right...the way to do this is simply pick a bullet and seat it as desired and send it in to have the chamber throated to match. I guess the reason I started this exercise is what MudRunner alluded to: if I have it throated specifically for one of the bullets and then that one doesn't shoot for some reason at any length, it may leave me having to load long for one of the others in order to get it to shoot. I'm probably overthinking. I just can't afford to do this twice, so I want it right the first time. [/QUOTE]
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