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I agree.

What about rotational velocity?

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Alf,
Could it have something to do with the incompressibility of fluids in the liquid phase, such as water and hydraulic line fluids?

And there is that phase change to bubbles of gas that is facilitated by the flat meplat.

Some of my simplistic thinking: ... The stagnation pressure piles up and drives the fluid in front of the nose. The hydraulic jack hammer splits the tissue asunder and any vaporization around the front of the bullet and trailing off to the sides envelops the bullet in the lower resistance gas.

Shoulder stabilization could still work in this cavitation too.

So, would a full diameter cylinder penetrate better than a smaller meplat solid?

How about if Mike at North Fork makes a .416 caliber 370 grain cylinder with the same driving bands as his .416/370gr FPS.

That sounds like a good test for the Steel Mistress.

Then the winner of that test gets a sharp edge to the flat meplat versus a rounded edge which we always seem to have for feeding ease.

Then winner of these two tests gets made in brass by Bridger for the ultimate champ penetrator.

I'll need more wood in the water if we keep adding wood to this fire.

quote:

But what I do not get or do not have an understanding of is why the cilinder does the opposite in primarily viscous media to air, when air is nothing but a fluid but with very low viscosity ?

Alf,

I think RIP is spot on with liquid Vs gas.

Proof of this is found in the distance a Mark VII 303 will carry. But on roos and pigs the results varied from.....they appeared not to be hit..to..their guts were all over the ground.

As a side note and only based on kangaroos and pigs....a conventional jacketed bullet loaded back to low velocity and low pressure in a big case is not as destructive as the same bullet at the same velocity loaded to maximum loads in a smaller case...eg 130 grain Speer Hollow point at about 2950-3000 f/s in 308 Winchester Vs loaded back to 3000 f/s in 300 Win and 300 Wby.

Mike

quote:

The low drag pointed projectile starts off by definition at point of impact with the lowest amount of nutation and assumes the best angle of attack, once it interacts with the viscous medium it becomes unstable WHY ?

Alf,
I believe that cavitation, or the lack there of, is actualy part of the reason, and here's why.The normal bending/buckling that takes place when a material is under pressure takes place in all bullets until the bubble is established. Delaying this deforms bullets and CAN reduce velocity by surface ablation. Surface ablation (mushrooming) actually would built a more effecent cavitation bubble.

Let's take this to a boat prop, just to make larger scale pictures.

have the boat hanging 1 foot out of the air on a quick release sling. Assumes conv. propeller boat

run the powertrain at the engine RPM settings (with the train engaged) for 20 knots. This boat is KNOWN to run at 20 knots, all day, and in fact, that's optimum speed for least fuel consumption. amoung other things, this means the propeller has it's LEAST/optimal cavitation possible for transfering power

while the boat is hanging in air, the forward movement caused by the prop is essentially NIL.

Now, with a super duper high speed camara we could see

if you dropped the boat suddenly into the water, (remembering the 20 knot assumption) and the prop instantly hits the water, slightly bends/twists as the blades hits the water, instantly fully cavitates (least possible eff. of transfering power) then quickly, but not instantly, "de"-cavitates and creates an effecient transfer, and our boat moves along.

WHY? Well, I thought this boat example was a nice earthy way of showing, and having everyone's head's nodding, that
1: materials deform on transitions
2: caviation is NOT instanteous

which leads me to assume that a long skinny bullet has more LENGTH of surface to be worked on by the inherent material strength/conditions of the animal BEFORE caviation is established. In fact, this may explain why imperfect caviation leads to tumbled bullets and vered paths.

Allow me to restate that: upon entering tissue, cavitation is established and (net-sum) stablized during the during ofthe life of the cavitation bubble. The establishment of cavitation is dependant on the physical characteristics of the bullet (these are open items). A flat bullet is shorter than a pointed bullet with a broader facing surface. The flat bullet establishes a cavitation bubble "quicker" and one that is more stable (shape and shape vs bullet diameter) than a pointy bullet. therefore a pointy bullet establishes a bubble slower (in reference to the depth of penetration vs bullet length)

which means the physical interactions of the colliding materials affect bullet deformation under impact, until the bubble is established, and long pointy bullets are not as physically tough, in cross section, than a flat point. The normal bending/buckling that takes place when a material is under pressure takes place in all bullets until the bubble is established. Should establishment be delayed/not occur, the bullet WILL sprawl, to a greater or lesser extent.

Wow, what a long way to go for that, but it could be an answer. Norbert would have better pictures of a bullets transistion from gas to liquid .
gentlemen, GAS and LIQUID two of the 4 basic physical states of matter, that they act like FLUIDS has no bearing on them. 4 states, btw, gas, liquid, solid, and (everyone forgets) plasma

jeffe

quote:

Originally posted by ALF:
500 gr:

The energy produced by Rotational velocity apparently is so small in magnitude that it plays very little or no role in wounding capacity or the form or shape of the wound cavity ( that according to Mc Pherson and others, I actually have two credible references that explain the math to show this)

I am not concerned about added energy resulting from rotational velocity. Rather, greater rotational velocity seems to contribute to bullet stability. Is there any study on that?

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The centre of gravity of a cylinder is at it's physical centre. The more pointy a bullet becomes, the further the CG moves back and the higher the twist requirement becomes for stability.

to 500 grains.

I've shot some of NEI's 645gn 458 bullets in a 458Win. at 1300 fps. The bullets came out of the mold with my alloy at 690+ grains and weighed 705 lubed and gaschecked. The Meplat diameter is .25" with a very short ogive, about .100 in length. The bullet hsa a bore riding nose, large crimp groove and 5 lube grooves. The bullet length is 1.790"

I can say with certainty that the bullet was not stable in flight as evidenced by some keyholes present in targets at 25 yards. No, not full profile keyholes but a goodly amount of tail wobble. In penetration testing these into wet newspaper stacks they would do turn and exit the sides of the stack within 32". The wound channel would indicate how far the bullet had laid down. This was observed at around 14". However, OCCASIONALLY they would go straight, and when they did, resulted in 66" of penetration.

Thought I'd through it out for you to chew on.
Thanks
Todd

Regarding exterior ballistics, yaw refers to the tilt of the bullets axis from the line of flight. Forces pushing on this will tend to cause a torque that will cause the projectile's axis to precess around the line of flight. If the spin is high, the bullet is "over-stabilized," and will tend to hold the axis even when the trajectory has changed a great deal, until the projectile can be almost perpendicular to flight (not really important until you're at long enough ranges for the trajectory to change significantly in direction as it lobbs in). Under-stabilized flight will allow the bullet to tip over with less force. Longer and skinnier bullets need more spin to stabilize them.

http://delivery.acm.org/10.1145/330000/320922/p89-zaroo...491&CFTOKEN=50847993

Given the above, what is going to happen when you suddenly hit harder material?

http://www-medlib.med.utah.edu/WebPath/TUTORIAL/GUNS/GUNBLST.html

Dan

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If the formula is correct, then the jam force goes to zero when the bullet's axis is perpendicular to the trajectory (cavitation axis). Is this correct? Are there other components to the force besides the jam force that you're looking at?

The rest of it (area * v^2 * target density * form-factor) looks pretty much like the rate momentum will be transferred to the target.

Other forces include viscous (proportional to velocity, usually more important at lower velocities). What kind of force is "friction"? A constant force in opposition to movement like a block on sandpaper?? Or, counting it relative to fluid absorbing momentum, it would look like area * velocity * friction -- ie viscosity by another name. I would not have expected solid (non-speed dependent) friction in a fluid...

Dan

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By this reckoning, the total rate of energy transfer to maintain the cavity is occurring through the jam force?

Also, even if the bullet key-holes, it strikes me that there still should be cavitation, but now you have the possibility of an extended "tip;" given forces tend to be additive, the force should be integrated over all the contact points that the jam force sees, including surfaces that aren't directly aligned with the force (where cos(theta) != 1)... No?

Dan