Zer0
is back to save the day!
It doesn't need to be that deep. Most pistol shrimp will accommodate themselves and make piles of sand wherever they feel necessary. With that being said, i would say 3" of sand is the minimum for a pistol shrimp. That's enough sand for them to either burrow, or to move the sand around to their liking. My pistol shrimp used to make piles of sand everywhere he went, so eventually the depth of sand in some areas was deeper than in other areas. The areas where it was deeper, is where he made his home. So it's not really a question of can it be done in a tank that small, but more or less, do you want sand piles all over your tank since you don't have enough sand for him to burrow in comfortably.