I believe I understand the point you are making, Angus.
My older brother was a tanker, stuck in Death Valley for his stint in the army. He first told me about the sabot rounds and their function when I was a teen, and yet had little knowledge of physics, but the concept fascinated me, as he said they did as claimed, both in the test videos he watched and then in the live fire exercises of which he was part. The pressure differential within the turret caused by the projectile did indeed suck all kinds of stuff through the tiny exit hole created by the projectile.
The confusions here are manifold though. First of all is the confusion of air vs fluids. Air IS a fluid. So fluid dynamics play a part. And what you describe, Angus, is a vacuum force which happens within the enclosed space of a tank turret when the mile-per-second depleted uranium projectile strikes and passes through the turret. The vacuum force created can easily be demonstrated in the fluid media of air or water as slow or rapid differentiations in pressure causing fluid movement. Drag a boat oar through water and watch what happens. Variations in pressure at the front and back of the oar cause fluid flow. Get on a plane, and the wings do the same thing, where the air over the top of the wing causes such a difference in pressure that the whole plane is lifted. Or my first real-world example of this on the scale of big things: in my girlfriend's crappy jeep driving down an interstate with a strong headwind that kept us from going over 60, until a passing semi swung into our lane nearly cutting me off, and the semi ended up dragging us about 80 miles, more or less, while I barely used the gas pedal.
These are the same forces that bullets cause in various fluids.
