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Rifles, Reloading, Optics, Equipment
Gunsmithing
Calculating Free Bore on 6.5 WSM?
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<blockquote data-quote="BoatTail" data-source="post: 1791259" data-attributes="member: 74670"><p>I need help figuring out how to calculate Freebore (FB) for a 6.5 WSM custom chamber reamer for a new rifle build I want to do.</p><p></p><p>Over the last few years I have had a number of custom chamber reamers made for various builds. In each case I either had a SAAMI reference chamber and drawing I could measure off of to make the FB adjustments I wanted or used the FB measurements for a similar cartridge I liked and trusted.</p><p></p><p>I'm now trying to determine the FB for a 6.5/300 WSM to allow the most case volume. I don't have a reference chamber to measure off of so need to make the calculation. The FB on the 6.5 PRC is a good reference (0.1879) but again wanted to make it optimum.</p><p></p><p>Here are my components:</p><ul> <li data-xf-list-type="ul">Remington 700 Short Action with a 3.110 extended well magazine and extended ejection port</li> <li data-xf-list-type="ul">Winchester 270 Brass resized to 6.5/300 WSM</li> <li data-xf-list-type="ul">Hornady 143gr ELD-X and Nosler 142gr Accubond Long Range bullets</li> </ul><p>This is one of the methods I was given to calculate Free Bore:</p><p></p><p>For a cartridge in 264:</p><p></p><p>Tools and components:</p><p><a href="https://www.longrangehunting.com/attachments/fb-tools-jpg.164541/" target="_blank"><img src="https://www.longrangehunting.com/data/attachments/155/155743-6e6c525df48e09df5883f4b2ed570ddc.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a></p><ul> <li data-xf-list-type="ul">Begin by cutting a notch out of the neck and shoulder of a donor case to be able to see where the bullet rides in the case at various COALs</li> <li data-xf-list-type="ul">Color the bullet nose of the bullets with a dark permanent marker</li> <li data-xf-list-type="ul">Subtract 0.002 from the cartridge bullet diameter (0.262)</li> <li data-xf-list-type="ul">Set your micro meter to 0.262 and mark/etch a circle around the bullet.</li> </ul><p><a href="https://www.longrangehunting.com/attachments/marking-262-jpg.164542/" target="_blank"><img src="https://www.longrangehunting.com/data/attachments/155/155744-4fbd34a0dd99dc3d51fb3a334c7b1027.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a></p><ul> <li data-xf-list-type="ul">Set the bullet in the case so the base of the neck and top of the boat tail of the bullet are aligned.</li> </ul><p><a href="https://www.longrangehunting.com/attachments/case-neck-boatail-junction-jpg.164543/" target="_blank"><img src="https://www.longrangehunting.com/data/attachments/155/155745-74c5139619af771dfa6121aad16bb403.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a></p><ul> <li data-xf-list-type="ul">Measure from the base of the case to the line marked earlier, just covering the line.</li> </ul><p><a href="https://www.longrangehunting.com/attachments/base-to-262-jpg.164544/" target="_blank"><img src="https://www.longrangehunting.com/data/attachments/155/155746-1ecea351ba733a20d77d4d99ecb60cad.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a></p><ul> <li data-xf-list-type="ul">Take that measurement and subtract 0.0477 ( I assume that this has something to do with subtracting the difference from Lead and Free Bore and were FB starts)</li> <li data-xf-list-type="ul">Take that measurement and subtract the case length (2.1 for my case)</li> <li data-xf-list-type="ul">This then gives you the free bore</li> <li data-xf-list-type="ul">My added step to to check the COAL to make sure it fits with clearance in the 3.110 magazine I bought from PTG.</li> </ul><p><a href="https://www.longrangehunting.com/attachments/base-to-262-jpg.164544/" target="_blank"><img src="https://www.longrangehunting.com/data/attachments/155/155746-1ecea351ba733a20d77d4d99ecb60cad.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a> <a href="https://www.longrangehunting.com/attachments/coal-2-90-jpg.164547/" target="_blank"><img src="https://www.longrangehunting.com/data/attachments/155/155749-c2c98a3321b9f795e0b8ec3bcf7fb2f6.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a></p><p></p><p>What I don't know is if I then add 0.02 to allow for bullet jump or not.</p><p></p><p>With the ELD-X and ABLR's this gives me a free bore around 0.252 for the custom reamer.</p><p></p><p>Using the measurements from the 2019 Berger Bullet Quick Reference Sheet I backed into the FB for a Berger 6.5 140 gr Elite Hunter and came up with 0.246 FB to ensure the top of the boat tail and bottom of the case neck met and thus use all of the neck for proper tension.</p><p></p><p>These FB dimensions seem excessive. Most of the drawings I have seen for the 6.5 WSM have a FB between 0.180 and 0.205 and as I said the 6.5 PRC FB is 0.1879.</p><p></p><p>How do you calculate the Free Bore for a new custom reamer?</p></blockquote><p></p>
[QUOTE="BoatTail, post: 1791259, member: 74670"] I need help figuring out how to calculate Freebore (FB) for a 6.5 WSM custom chamber reamer for a new rifle build I want to do. Over the last few years I have had a number of custom chamber reamers made for various builds. In each case I either had a SAAMI reference chamber and drawing I could measure off of to make the FB adjustments I wanted or used the FB measurements for a similar cartridge I liked and trusted. I'm now trying to determine the FB for a 6.5/300 WSM to allow the most case volume. I don't have a reference chamber to measure off of so need to make the calculation. The FB on the 6.5 PRC is a good reference (0.1879) but again wanted to make it optimum. Here are my components: [LIST] [*]Remington 700 Short Action with a 3.110 extended well magazine and extended ejection port [*]Winchester 270 Brass resized to 6.5/300 WSM [*]Hornady 143gr ELD-X and Nosler 142gr Accubond Long Range bullets [/LIST] This is one of the methods I was given to calculate Free Bore: For a cartridge in 264: Tools and components: [URL='https://www.longrangehunting.com/attachments/fb-tools-jpg.164541/'][IMG]https://www.longrangehunting.com/data/attachments/155/155743-6e6c525df48e09df5883f4b2ed570ddc.jpg[/IMG][/URL] [LIST] [*]Begin by cutting a notch out of the neck and shoulder of a donor case to be able to see where the bullet rides in the case at various COALs [*]Color the bullet nose of the bullets with a dark permanent marker [*]Subtract 0.002 from the cartridge bullet diameter (0.262) [*]Set your micro meter to 0.262 and mark/etch a circle around the bullet. [/LIST] [URL='https://www.longrangehunting.com/attachments/marking-262-jpg.164542/'][IMG]https://www.longrangehunting.com/data/attachments/155/155744-4fbd34a0dd99dc3d51fb3a334c7b1027.jpg[/IMG][/URL] [LIST] [*]Set the bullet in the case so the base of the neck and top of the boat tail of the bullet are aligned. [/LIST] [URL='https://www.longrangehunting.com/attachments/case-neck-boatail-junction-jpg.164543/'][IMG]https://www.longrangehunting.com/data/attachments/155/155745-74c5139619af771dfa6121aad16bb403.jpg[/IMG][/URL] [LIST] [*]Measure from the base of the case to the line marked earlier, just covering the line. [/LIST] [URL='https://www.longrangehunting.com/attachments/base-to-262-jpg.164544/'][IMG]https://www.longrangehunting.com/data/attachments/155/155746-1ecea351ba733a20d77d4d99ecb60cad.jpg[/IMG][/URL] [LIST] [*]Take that measurement and subtract 0.0477 ( I assume that this has something to do with subtracting the difference from Lead and Free Bore and were FB starts) [*]Take that measurement and subtract the case length (2.1 for my case) [*]This then gives you the free bore [*]My added step to to check the COAL to make sure it fits with clearance in the 3.110 magazine I bought from PTG. [/LIST] [URL='https://www.longrangehunting.com/attachments/base-to-262-jpg.164544/'][IMG]https://www.longrangehunting.com/data/attachments/155/155746-1ecea351ba733a20d77d4d99ecb60cad.jpg[/IMG][/URL] [URL='https://www.longrangehunting.com/attachments/coal-2-90-jpg.164547/'][IMG]https://www.longrangehunting.com/data/attachments/155/155749-c2c98a3321b9f795e0b8ec3bcf7fb2f6.jpg[/IMG][/URL] What I don't know is if I then add 0.02 to allow for bullet jump or not. With the ELD-X and ABLR's this gives me a free bore around 0.252 for the custom reamer. Using the measurements from the 2019 Berger Bullet Quick Reference Sheet I backed into the FB for a Berger 6.5 140 gr Elite Hunter and came up with 0.246 FB to ensure the top of the boat tail and bottom of the case neck met and thus use all of the neck for proper tension. These FB dimensions seem excessive. Most of the drawings I have seen for the 6.5 WSM have a FB between 0.180 and 0.205 and as I said the 6.5 PRC FB is 0.1879. How do you calculate the Free Bore for a new custom reamer? [/QUOTE]
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