Once compacted, it cannot be crushed together any further. A bullet hit will disperse in all directions, increasing the amount of mass involved in stopping the bullet, therefore limiting its progress.
Command troops used strategically positioned sand bags to protect their parachuted lightweight vehicles against mines and gunfire. (The sack under the seat was called the ball saver, after pinball games
)
Sand has no structural strength whatsoever, but cannot be compressed either. It does catch bullets and whatnot.
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2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
lifetime FE over 0.2 Gmeter or 0.13 Mmile.
For confirmation go to people just like you.
For education go to people unlike yourself.