I think there's a video of a Cartbon Cub on tundras doing it in >20 feet.
Mind you, I have see a Beaver take off vertically and fly backwards. OK, it was without a pilot.
Two mistakes were made that day. A maintenance crew had positioned the Beaver in the middle of the hanger for maintenance - they for got to place the "lift killers" on the wings (ground equipment - simply planks that we'd strap to the upper surfaces of the wings. The hangar front doors were open as someone was moving other Beavers out and it was a windy day.
Mistake #2, on the flingwing end of the hangar, some fool decided to open the other hangar doors.
Imagine "venturi". The wind was straight on and with the venturi effect, we had >60 kts.
Imagine a crowd of headless chickens. That Beaver was off its wheels (oh yes, mistake #3 - no control locks)
Thing is, the rear doors were not yet fully open. Damaged tailplane, damaged roof (smashed into the ceiling crane hook), lots of loose and light equipment blown all over the place and a couple of new private soldiers.