I'd be more apt to be afraid of tank being struck by lighting then exploded by gunshot....
....one more thing for the OP to worry about.
The reason I say this is I had a tree in the backyard that set about 20ft. from our tank. Tree took a direct lighting hit. A few days later the grass turned brown fingering out from the trunk of the tree where the tree root base went. One very nice brown strip went straight under propane tank.
There's a company going around in these parts that install underground tanks and have been hyping the non-safety issue's of above ground tanks. Haven't seen any rush for existing above ground tank owners to convert but there have been a few house's built in the area that's had their tank inst'd underground.
At any rate, periodically inspecting lines, valves etc...the tanks are rounded , made of thicker steel and I've never worried about it.