The problem:
From many recent threads it is now common wisdom, that flat nose bullets with a distinct meplat show deeper penetration in game or aqueous targets than conventionel round nose bullets.
But an explanation for this behaviour is discussed somewhat puzzling.
Two theories are cited often:
a). The (super)cavitation theory and
b). The shoulder stabilisation theory.

The theories:
a).The supercavitation theory assumes, that at the edge of the meplat a gaseous bubble is formed, which envelops the whole bullet, preventing a contact with the tissue and minimize friction at the shank of the bullet. The most important effect is, that, because friction in the dense target is less than it would be with a direct contact, the rotation generated by the twist of the barrel is kept active. So the bullet maintains its gyroscopic stabilization in the tissue. Therefore it shows much deeper straight line penetration. More on supercavitation here.
b). Shoulder stabilization assumes, that at a bullet which starts tumbling, the point of maximum pressure (stagnation pressure) shifts a little towards the forward moving edge and so pushes it back to the normal flight direction.
1994 this idea was published by Kneubuehl and propagated by Möller in the web. This idea is simple and even Alf took it for granted. They claimed shoulder stabilization for rotating and non rotating bullets. When in 1999 I published my cavitation theory and later I asked M. and others to give some experimental evidence or basic scientific calculation. But up to now I never saw a stringent proof or demonstration of this shoulder stabilization. In 2004 Kneubuehl described SS only for short cylindrical bullets with a plain frontal area, flying in air.
The reality:
For long hunting bullets with a small meplat even the simple model doesn´t make sense: A little shift of the stagnation point will tip the bullet for tumbling.(see fig.) But it shows exceptional straight line penetration.
Shoulder stabilization is possible, when the center of gravitation is close to the front and the object is relative broad with respect to its moving direction and has a short axis. Spacecraft like Apollo are stabilized by this effect, falling leafes and other objects moving in a flow, try to achieve a position where the CoG is near the surface (broadside, not small area ahead.)
Hemispherical RN bullets are stabilized for a shallower penetration depth, because also cavitation occurs, but this is not as stable as with a sharp edged meplat. With shoulder stab. a stabilization should be impossible.
SS is claimed to be effective also in air. I never heard about long hunting bullets stable without gyroscopic stabilization.
I made experimental test to enlighten this issue:
Shots into my 1.8 gallon water container, 7" water path:
.38 cylinder (wadcutter), prepared to have the CoG back from the geometrical center, shot from a smooth bore: tumbled immediately after entering the container.
The same effect with a slug from a shotgun, where I removed the rear elements used for the arrow stabilization.

This is a very simplified overview and my limited english may also leave some questions open.

BTW: Stabilisation mechanism in hard, nonaqueous material is different.
Penetration depth in hard material (plywood, particle board) is somewhat less than with RN, depending on the design. The SuperPenetrator is about 10% less in particle board.

Kneubuehl, a knowlegdable ballistician, says: In water bullets behave very similar as in biological tissue. So especially RIP should carry on.

Sorry, I am off for africa the next five weeks.

Norbert, where are you hunting? What company?

quote:

Originally posted by 500grains:
Norbert, where are you hunting? What company?

No company. I am going as a guide at different places in Namibia. In april I hunted with Buzz for tuskless in Dande south. Excellent as usual.

Norbert:

What case do you recommend for your 9.3 SP bullet?

Will the 9.3X66 SAKO seat the bullet properly?

Thanks