How fast does a balloon drift?
Well, it covers the ground at windspeed but it's airspeed is always zero. Of course.
Hydrogen filled Zeppelins in WW1 were the very devil to shoot down even when the right kind of incendiary ammunition was found to set them alight - sometimes, and that won't work on helium.
Shooting holes in a blimp with a gun would have no discernable effect for days, so small are the holes and so large the volume of gas. The differential pressure in the ballonets is so close to ambient that gas doesn't want to leak quickly out of even quite big holes. Downing a blimp isn't all that easy, I suspect. It won't pop like a party balloon you know!