On Mon, Jun 29, 2015 at 2:39 AM, Richard Aiken <raikenclw@gmail.com> wrote:

On Sun, Jun 28, 2015 at 8:14 AM, Grimmund <grimmund@gmail.com> wrote:
Why would you need the sabot to drop away? I mean, in a vacuum,
there's no atmospheric drag due to the increased cross section of the
projectile....

The advantage of the squeezed/tapered bore effect (which is effectively duplicated through the use of APDS ammo in modern cannon) is the increase in muzzle velocity and consequent increased range/penetration.

I'm frankly not sure how a sabot dropping away duplicates the effects of squeezing the caliber of the fired round down by ~30%. I *suspect* it's because the sabot fills out the larger caliber but is substantially lighter, so the acceleration provided by the gasses of the bursting charge is effectively increased in the final fraction of a second of firing, as the sabot falls away just outside the muzzle.

The KE of the projectiles parts is in the ratio to the mass of the parts of the projectile.

If you have a 90 gram dart and a 10 gram sabot, then the dart has 90% of the KE of the muzzle energy.

In chem powered slug throwers, chamber pressure and chemistry places a cap on energy per unit of chamber cross section. A 10mm bore has less room for powder than a 20mm bore, and even if you used a more powerful propellent to get the same energy in the smaller caliber, you'd be raising the chamber pressure and need much stronger and/or heavier breech/chamber to restrain them.

What a DS round does is let you use an oversized chamber to get more propellant without hitting the chamber pressure issue... but then concentrate the energy into a smaller projectile.

Why not just use a solid projectile of the larger diameter?

KE=1/2 M V^2.

A lighter projectile is going to be going faster for the same energy input, and that means a flatter trajectory with more penetration... and if it's a smaller diameter, a more focussed hit for even more penetration.

Yes, you'll lose the some of the energy with the sabot, but the hope is you gain increased chance to hit and penetration with the faster projectile.

In space, I don't think you need the fins.. unless it's hyper-hyper fast, where random particle density begins to matter. I think I saw someone do calcs above with a near-light speed projectile.

For a space-to-space gun, I could see something where the "sabot" is actually a thing like charges on a mortar shell, which fire to provide some course correction. Or like the side-firing rockets on a TOW missile, same reason.

Or a projectile like a Minie Ball, with a "skirt" that flares out to provide the gas seal.