Just curious pj, what really happens if a round is shot through a window or something?

According to MythBusters, nothing much. The window gets a hole, the cabin pressure drops somewhat, unless you put your hand over the hole. Ditto results if you blast a hole in the fuselage. But if you set off a hunk of explosive, that changes things a bit.

Brian

The fuselage is a stressed member of the pressurized tube. It could handle a bullet hole in the skin, but a larger hole, that was jagged, would cause cracks to run every which way.
A few years ago a 737, island hopping in Hawaii, lost the upper half of the cabin for about 15 or 20 feet behind the cockpit and a stewardess was sucked out. The pilot managed to land with no further injuries (damn good flying), although the passengers were pretty well buffeted and I suspect, sitting in poop.
The subsequent investigation blamed the cause on a SCRATCH in one of the skin panels, that had cracked. When the crack gave way to the pressure inside the cabin, it ripped open and started a chain reaction with ajoining panels in all directions, until it reached the seams where the plane was assembled. The seams are doubly reinforced because when the sections are made, They have a stringer (horz.) or rib (vertical) along the edge for manufacturing and handling.
In other words.....Yeah, what BrianR said.
:D

to further knowledge, the air pressure inside a passenger jet flying at 30,000 feet (cruising altitude) is approximately 8 psi.

Blowouts are all but impossible, but it IS possible to lose a portion of the plane in what must appear to be a "blowout" and what is actually the slipstream (about 600 mph) getting inside and tearing off a chunk of important parts.

So yeah, what Bruce said. ;)

Brian

And you can't cause an explosion at a gas station with a cell phone.