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Improving the 308 Win performance
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<blockquote data-quote="nralifer" data-source="post: 2737725" data-attributes="member: 94556"><p>From your description of an Elk hunt and the trouble and expense one goes through to do it, one wonders why do it at all, but yet we all dream of doing it at least once if, not repeatedly. That is why we spent 2 years testing various hollow point designs for reliability of expansion and integrating a tip to preserve BC. The two biggest factors that influenced the final design were material ductility and force concentration. In the end we realized that custom tooling was necessary to execute the design we knew would open reliably. Pure copper is not easy to machine but it has the right ductility so that the petals will bend back at a 1.5 caliber diameter, and the copper could be made thin enough to open reliably. The aluminum tip, or any tip for that matter, actually hinders expansion, but aluminum it does one crucial function and that is it preserves BC and aids the initial puncture of the skin without any deformation of the meplat. Once that happens the force of impact transmitted to the copper hollow point enlarges the hollow diameter loosening the tip such that it falls out and fully exposes the hollow to the in-rush of soft tissue and ripping of the copper along weak cuts along the length of the hollow causing a predictable petaling pattern. The pure copper, being softer than free machining copper bends back rather than fracturing. The petals are sharp and take advantage of the rotational motion of the bullet imparted to it by the barrel rifling (typically over 200,000RPM). That motion, coupled with the fact that the bullet will also have a linear force of several thousands of foot pounds of force distributed over 1.5 caliber diameter, causes the expanded bullet to drill and forcibly displace tissue such that a large temporary wound cavity is created and penetration is maximized. Thus, high impact velocities as well as low impact velocities are associated with 30+ inch penetrations regardless of the angle of impact. In all instances the bullet shank is preserved so that even in the extreme impact (say less that 50 yds) where the petals may shear off after 5-6" of penetration, the surviving shank tumbles causing massive organ damage. The high BC relative to bullet weight means that over distance the bullet sheds its energy at a lower rate, meaning it will travel further before reaching the recommended minimum impact velocity. Thus the "performance envelope" of the bullet is much wider than conventional lead core bullets or copper bullets of similar weight but lower BC.</p></blockquote><p></p>
[QUOTE="nralifer, post: 2737725, member: 94556"] From your description of an Elk hunt and the trouble and expense one goes through to do it, one wonders why do it at all, but yet we all dream of doing it at least once if, not repeatedly. That is why we spent 2 years testing various hollow point designs for reliability of expansion and integrating a tip to preserve BC. The two biggest factors that influenced the final design were material ductility and force concentration. In the end we realized that custom tooling was necessary to execute the design we knew would open reliably. Pure copper is not easy to machine but it has the right ductility so that the petals will bend back at a 1.5 caliber diameter, and the copper could be made thin enough to open reliably. The aluminum tip, or any tip for that matter, actually hinders expansion, but aluminum it does one crucial function and that is it preserves BC and aids the initial puncture of the skin without any deformation of the meplat. Once that happens the force of impact transmitted to the copper hollow point enlarges the hollow diameter loosening the tip such that it falls out and fully exposes the hollow to the in-rush of soft tissue and ripping of the copper along weak cuts along the length of the hollow causing a predictable petaling pattern. The pure copper, being softer than free machining copper bends back rather than fracturing. The petals are sharp and take advantage of the rotational motion of the bullet imparted to it by the barrel rifling (typically over 200,000RPM). That motion, coupled with the fact that the bullet will also have a linear force of several thousands of foot pounds of force distributed over 1.5 caliber diameter, causes the expanded bullet to drill and forcibly displace tissue such that a large temporary wound cavity is created and penetration is maximized. Thus, high impact velocities as well as low impact velocities are associated with 30+ inch penetrations regardless of the angle of impact. In all instances the bullet shank is preserved so that even in the extreme impact (say less that 50 yds) where the petals may shear off after 5-6” of penetration, the surviving shank tumbles causing massive organ damage. The high BC relative to bullet weight means that over distance the bullet sheds its energy at a lower rate, meaning it will travel further before reaching the recommended minimum impact velocity. Thus the “performance envelope” of the bullet is much wider than conventional lead core bullets or copper bullets of similar weight but lower BC. [/QUOTE]
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