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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
SHERMAN MEGA LINE
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<blockquote data-quote="brittf" data-source="post: 2428685" data-attributes="member: 121792"><p>So, I have been doing some detailed drawings with Sherman chambers and various bullets to better understand jump and bullet selection.</p><p></p><p>I understand no one has the Mega brass yet, since it isn't available, but I would appreciate some information on jump for those of you who have the Sherman Max.</p><p></p><p>My CAD drawings and calculations show that the 7mm Sherman Max chamber is very well sized for the 180 and 190 gr Berger bullets, with the bearing surface just inside the neck/shoulder junction at 'touch'. That is essentially 'perfect' if you want full neck engagement with long bullets, but want to avoid the donut problem. You can increase jump to 0.020"-0.060" without the bullet taking up much (if any) powder 'real estate'.</p><p></p><p>When I play around with the 7mm Sherman Mega (based off a 'long-necked' 300 WSM), I find a similar situation where the chamber is essentially 'perfect' for the 180 to 197 gr bullets, in the STANDARD medium-action (0.205" Freebore) setup. The neck is longish, so even the shorter bullets have plenty of neck engagement (down to maybe 170 gr or so).</p><p></p><p>However, since I am building a LONG action, Rich suggested the LONG reamer (0.305" Freebore) setup for my Mega build. The extra 0.100" of Freebore length reduces the neck engagement by a similar amount on any bullet. For the very long bullets (190, 195, 197 gr) it seems to work out just fine - if I plan on 0.020-0.040" jump, I still have pretty good neck engagement (maybe 85% of bore diameter). That should work. However, once you drop below the 190 gr bullets, either the neck engagement gets pretty small (0.200") or the jump gets excessive (0.100").</p><p></p><p>Now, this isn't a problem if the bullets and chambers LIKE a good jump. However, I am learning my craft from a well-known Benchrest and F-Class gunsmith, and he is all about small (to no) jump and good, long neck engagement. So, I am at a crossroads...</p><p></p><p><strong>What kind of jump are you guys running with, in particular, the Max cartridges? </strong> Are we talking 0-0.020" or much larger? Historically, overbore magnums had a LOT of jump to reduce chamber pressure and still get high speeds. Does the Max and, especially, the Mega fall in this category?</p><p></p><p>Thank you in advance for your time and consideration.</p><p></p><p>Regards,</p><p>brittf</p></blockquote><p></p>
[QUOTE="brittf, post: 2428685, member: 121792"] So, I have been doing some detailed drawings with Sherman chambers and various bullets to better understand jump and bullet selection. I understand no one has the Mega brass yet, since it isn't available, but I would appreciate some information on jump for those of you who have the Sherman Max. My CAD drawings and calculations show that the 7mm Sherman Max chamber is very well sized for the 180 and 190 gr Berger bullets, with the bearing surface just inside the neck/shoulder junction at 'touch'. That is essentially 'perfect' if you want full neck engagement with long bullets, but want to avoid the donut problem. You can increase jump to 0.020"-0.060" without the bullet taking up much (if any) powder 'real estate'. When I play around with the 7mm Sherman Mega (based off a 'long-necked' 300 WSM), I find a similar situation where the chamber is essentially 'perfect' for the 180 to 197 gr bullets, in the STANDARD medium-action (0.205" Freebore) setup. The neck is longish, so even the shorter bullets have plenty of neck engagement (down to maybe 170 gr or so). However, since I am building a LONG action, Rich suggested the LONG reamer (0.305" Freebore) setup for my Mega build. The extra 0.100" of Freebore length reduces the neck engagement by a similar amount on any bullet. For the very long bullets (190, 195, 197 gr) it seems to work out just fine - if I plan on 0.020-0.040" jump, I still have pretty good neck engagement (maybe 85% of bore diameter). That should work. However, once you drop below the 190 gr bullets, either the neck engagement gets pretty small (0.200") or the jump gets excessive (0.100"). Now, this isn't a problem if the bullets and chambers LIKE a good jump. However, I am learning my craft from a well-known Benchrest and F-Class gunsmith, and he is all about small (to no) jump and good, long neck engagement. So, I am at a crossroads... [B]What kind of jump are you guys running with, in particular, the Max cartridges? [/B] Are we talking 0-0.020" or much larger? Historically, overbore magnums had a LOT of jump to reduce chamber pressure and still get high speeds. Does the Max and, especially, the Mega fall in this category? Thank you in advance for your time and consideration. Regards, brittf [/QUOTE]
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