Just a little something i threw together, is extremely effective for mining operations ;)

Key:
INR / Impulse, Needs Redstone
IAA / Impulse, Always Active

CNR / Chain, Needs Redstone
CAA / Chain, Always Active

RNR / Repeating, Needs Redstone
RAA / Repeating, Always Active

A command will follow the stated command block type, and you will need to past the command into said block. With that out of the way:

Destruction Bombs

RAA:
testfor @e[type=snowball]
CAA:
execute @e[type=snowball] ~ ~ ~ fill ~1 ~1 ~1 ~-1 ~-1 ~-1 air 0 destroy

Out to side of first repeating block:

unpowered comparator facing left/right of the repeating block
repeater / 1st setting
RNR:
kill @e[type=snowball]

I've attached a picture to help demonstrate. I didn't feel like a world download was necessary for this, it's pretty easy to build ^-^