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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
is copper jacket spinning around lead core during flight
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<blockquote data-quote="QuietTexan" data-source="post: 2276636" data-attributes="member: 116181"><p>It seems like there would be a convective transfer issue where the lead core is not evenly heated and would not uniformly liquify. There would be a boundary layer formed between the jacket and solid portion of the core, and as small as bullets are a shear flow layer would form and the relatively high viscosity of lead at its melting point would resist the shearing motion, so the non-uniformly liquified lead core would still rotate along with the jacket. This might be why bonded jacketed bullets perform better than straight cup and core bullets at higher impact velocities/ faster twist barrels, because the core and jacket have a chemical bond that has to be overcome, not simply a convective heat transfer from one metal to another.</p><p></p><p>I'm not convinced the core actually melts, I don't know how to calculate it but I'm sure some engineer could do the math on how much heat the core absorbs by convection over the relatively short time window of the bullet's flight. Think of the RPMs of a 36gn Varmint Grenade going 4000FPS out of a 12-twist 22-250. Those bullets hold together, and they function by having a sintered metal core that fragments when it hits the target. I'm sure the melting point of the copper-tin powder is higher than lead, but there's also significantly less mass available to absorb heat from the shot. If the core was melting it wouldn't explosively fragment the way that we see them do in ballistic gel.</p></blockquote><p></p>
[QUOTE="QuietTexan, post: 2276636, member: 116181"] It seems like there would be a convective transfer issue where the lead core is not evenly heated and would not uniformly liquify. There would be a boundary layer formed between the jacket and solid portion of the core, and as small as bullets are a shear flow layer would form and the relatively high viscosity of lead at its melting point would resist the shearing motion, so the non-uniformly liquified lead core would still rotate along with the jacket. This might be why bonded jacketed bullets perform better than straight cup and core bullets at higher impact velocities/ faster twist barrels, because the core and jacket have a chemical bond that has to be overcome, not simply a convective heat transfer from one metal to another. I'm not convinced the core actually melts, I don't know how to calculate it but I'm sure some engineer could do the math on how much heat the core absorbs by convection over the relatively short time window of the bullet's flight. Think of the RPMs of a 36gn Varmint Grenade going 4000FPS out of a 12-twist 22-250. Those bullets hold together, and they function by having a sintered metal core that fragments when it hits the target. I'm sure the melting point of the copper-tin powder is higher than lead, but there's also significantly less mass available to absorb heat from the shot. If the core was melting it wouldn't explosively fragment the way that we see them do in ballistic gel. [/QUOTE]
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is copper jacket spinning around lead core during flight
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