On Wed, Jul 08, 2015 at 06:56:15AM -0400, Richard Aiken wrote:
> But you *want* to increase the slug's drag along the bore.

No, you really don't.

> This is what let's you build up a higher effective pressure against
> the shrinking-diameter slug as it travels.

Yes, the pressure will be higher because less of the gas thermal
energy is being converted into kinetic energy.  What's more, the
reduced area means less accelerating force for a given pressure.  Both
factors are negative effects, not positive.

> That increased pressure is what increases the muzzle velocity so
> markedly.

It doesn't.  I'm not sure what configurations you're comparing the
muzzle velocity for in your head, but it seems to be something
completely irrelevant to the discussion at hand.

> To achieve the same muzzle velocity without squeezing, you would
> need a relatively much larger cannon bore and a consequently much
> larger round.

Or a much simpler non-collapsing sabot without the energy wasted to
friction.

- Tim