What causes a soft point to expand?

[Unobtanium]

It's a simple question with, I suspect, a complex answer. Many people will say velocity, and when comparing a round to itself, this is correlary...but is it causative?

Bullet A will expand out to XXX yards....so many cap that as velocity induced. Surely it tracks.

Then we introduce bullet C, which has identical construction front of the cannelure to bullet A...but with the edition of much more weight and much higher BC.

Now let's assume that both bullets impact at 250 yards. They are both travelling at the same speed because the lower initial velocity of C has been offset by C having a much higher BC. However...bullet C is carrying 20% more energy...

...will bullet C expand more than bullet A, or will they expand the same, and will bullet C expand to further distances than bullet A, if their velocities are similar but the KE of C is significantly higher?

This question may seem unrealistic, but in the case of the 62 and 75gr gold dot in .223, it is infinitely germane to understanding the long distance terminal effects of these projectiles. ..

So again, which causes expansion in soft point rifle projectiles...velocity, or KE?

[TiroFijo]

I would guess that regarding expansion impact velocity rules over the other variables (you said both bullets have identical construction front of the cannelure). So it would be impact velocity (depending on initial velocity, range and BC) what determines, or influences the most, if the bullet expands and how much, and not KE or momentum.

[voodoo_man]

Paging doc....

[noylj]

Design and velocity.
meplate size
scoring of jacket
thickness of jacket
impact velocity
impact energy transfer
and probably many other variables.

[Unobtanium]

Design and velocity.
meplate size
scoring of jacket
thickness of jacket
impact velocity
impact energy transfer
and probably many other variables.

Bullets are identical forward of cannelure, in my real world example.

[357carbine]

"Bullets are identical forward of cannelure, in my real world example."
Lazy designer. Probably drives a VW Bug with a Rolls Royce front end.

"So again, which causes expansion in soft point rifle projectiles...velocity, or KE?"
Bullets are designed, base to tip, to work within a velocity "window." And, don't forget that there is speed of expansion too (varmint vs. controlled).
That's my guess.

[michael1778]

Stressing the soft point metal up beyond its yield stress. That is what causes the deformation. What induces/causes the stress in the metal? Depends on the target. If you hit a steel plate it's the immobile steel target with the bullet piling up on top of it. In "soft targets" the hydrodynamics or collision with bone, etc is what causes the point to yield and deform. Velocity is a key variable in hydrodynamic pressure, so that's why it is the often cited parameter for soft point or hollow point performance.