And more detail yet. This too from rec.aviation.piloting:

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The comments below are applicable to modern commercial Pax A/C. Anyone
familiar with the structure of an A/C will immediately ROFL at the
idea of a 9mm bullet penetrating the external skin if fired from
inside the cabin.

It would take a substantially more powerful weapon than a 9mm to cause
a "Window Failure", even then impact would have to be near 90 degrees
because of their "Plug design, plus they are thicker in the center
than the edge This curvature is on the inside.

The same applies to a bullet exiting through the A/C skin. Consider
between what is seen as the interior cabin wall & the "External Skin"
of the A/C is a layer of insulation, assorted wiring, plumbing in
some places, plus untold ribs, stiffeners, & other assorted structural
components all of which have some "Curvature" to them. All these
components are riveted together through "Lap Joints". All
joints/connections are sealed with "Sealant" of varying strengths.

The structure of an A/C is designed to flex, expand, & contract as the
A/C goes thru pressurization/de-pressurization cycles.

There are a few places a "Very High Velocity Bullet" of large caliber
could possibly exit the external skin if it the internal point of
impact was at a "very specific angle, very close to 90 degrees to
external skin" if fired from close range internally. Consider all the
materials described above a bullet would have to impact/penetrate,
without its path being diverted by some degree of ricochet.

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(Again: the above is quoted from rec.aviation.piloting)


all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com