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Absolutely true that more velocity is better for more expansion, but HP's, especially modern HP's will absolutely expand better in flesh than the same weight/diameter/velocity LRN or LFP, if we're talking about "expansion in flesh".
Living flesh is over 90% liquid, which is the basis for "hydrostatic shock" in wounds ("Hydro" = "water"). With a HP bullet, unless it's cavity is plugged with cloth, etc, you get violent hydraulic pressure pushing on the insides of the cavity, forcing it out and open. As it opens, it becomes more dimensionally susceptible to these pressures and the opening 'cycle' continues as long as it's moving with decent velocity. With enough velocity, the pressure on the outside of the bullet is actually less than on the inside, due to the elasticity of tissue; the 'shock' ripple helps reduce exterior pressure on the bullet. As it expands (and slows) to the point where directional momentum is overcome by bullet-base momentum (it basically ends up unstable, as an arrow flying feathers-first would) it generally veers or "detours" from its original path until its energy is spent.
[This is why things that maximize hydraulic effects (such as the post in the Hydra-shock that helps 'push' liquid toward the cavity sides, the thin-wall striations of the Black Talon, and the larger, more straight-inside-wall designs of even more traditional HP designs) work better than the older, smaller-cavity ones.]
This is assuming no bone impact, obviously. With a bone hit, an HP will become deformed and actually expand less overall than if it just travels through "flesh". With a bone hit, though, you do get the additional trauma of multiple bone fragment "projectiles", so it offets (at least somewhat) the reduced performance of the HP itself.
A LRN or LFP bullet is certainly softer and easier to deform manually, but hydraulically (as in flesh) an HP bullet has advantages a solid (even SP) bullet doesn't. (Especially at the velocity lead bullets are generally driven.) The LRN or LFP is almost literally being 'held' in it's original form, prevented from violent deformation, by the existence of equal hydraulic pressure on all sides, unless/until it encounters bone or some other "non-flesh" impediment. Then its deformed shape allows response to hydraulic pressures, and it either deforms (or detours) until its energy is spent.
This hydraulic component must be recognized and accepted in bullet design and choice. Even Glasers (with their FMJ profile) use hydraulic force to do their work; they just reverse certain parts of the equation. Instead of the body's liquid acting on the resisting metal walls of an HP design, the Glaser bullet brings with it its own hydraulic component to the situation. As the flesh drags at the outside of the bullet jacket (in the first inch or so of penetration), the liquid inside the jacket (because it's a liquid) begins to act separately of the jacket. It then forces itself out the front of the bullet's decelerating jacket, carrying with it its shot payload. That's why a Glaser works so well on flesh, but not on "hard" targets; concrete block, sheet metal airplane skins, etc. On a hard target, the hydraulic effect is very much (if not completely) diminished, and while the bullet itself naturally has the same "energy" (same mass and velocity), it wastes that energy in a non-productive way.
I guess what I'm saying, is that while energy (i.e. 'velocity') is definitely a very important factor, it's not the only factor. The effects on a given target type can very greatly, even with the same caliber/energy combination.
Living flesh is over 90% liquid, which is the basis for "hydrostatic shock" in wounds ("Hydro" = "water"). With a HP bullet, unless it's cavity is plugged with cloth, etc, you get violent hydraulic pressure pushing on the insides of the cavity, forcing it out and open. As it opens, it becomes more dimensionally susceptible to these pressures and the opening 'cycle' continues as long as it's moving with decent velocity. With enough velocity, the pressure on the outside of the bullet is actually less than on the inside, due to the elasticity of tissue; the 'shock' ripple helps reduce exterior pressure on the bullet. As it expands (and slows) to the point where directional momentum is overcome by bullet-base momentum (it basically ends up unstable, as an arrow flying feathers-first would) it generally veers or "detours" from its original path until its energy is spent.
[This is why things that maximize hydraulic effects (such as the post in the Hydra-shock that helps 'push' liquid toward the cavity sides, the thin-wall striations of the Black Talon, and the larger, more straight-inside-wall designs of even more traditional HP designs) work better than the older, smaller-cavity ones.]
This is assuming no bone impact, obviously. With a bone hit, an HP will become deformed and actually expand less overall than if it just travels through "flesh". With a bone hit, though, you do get the additional trauma of multiple bone fragment "projectiles", so it offets (at least somewhat) the reduced performance of the HP itself.
A LRN or LFP bullet is certainly softer and easier to deform manually, but hydraulically (as in flesh) an HP bullet has advantages a solid (even SP) bullet doesn't. (Especially at the velocity lead bullets are generally driven.) The LRN or LFP is almost literally being 'held' in it's original form, prevented from violent deformation, by the existence of equal hydraulic pressure on all sides, unless/until it encounters bone or some other "non-flesh" impediment. Then its deformed shape allows response to hydraulic pressures, and it either deforms (or detours) until its energy is spent.
This hydraulic component must be recognized and accepted in bullet design and choice. Even Glasers (with their FMJ profile) use hydraulic force to do their work; they just reverse certain parts of the equation. Instead of the body's liquid acting on the resisting metal walls of an HP design, the Glaser bullet brings with it its own hydraulic component to the situation. As the flesh drags at the outside of the bullet jacket (in the first inch or so of penetration), the liquid inside the jacket (because it's a liquid) begins to act separately of the jacket. It then forces itself out the front of the bullet's decelerating jacket, carrying with it its shot payload. That's why a Glaser works so well on flesh, but not on "hard" targets; concrete block, sheet metal airplane skins, etc. On a hard target, the hydraulic effect is very much (if not completely) diminished, and while the bullet itself naturally has the same "energy" (same mass and velocity), it wastes that energy in a non-productive way.
I guess what I'm saying, is that while energy (i.e. 'velocity') is definitely a very important factor, it's not the only factor. The effects on a given target type can very greatly, even with the same caliber/energy combination.