Hello!I present you the iron man command!This is tested and should work.It'll take quite along time to install it into your world, so just listen to the steps to be quicker.Ok step 1.Type in chat:/give @p command_block
2.Type in it /summon FallingSand ~ ~1 ~ {Block:command_block,Time:1,DropItem:0}
3.Then power it.
4.In the command block you see on top of that type in:
/execute @e[type=Arrow] ~ ~ ~ /summon PrimedTnt
5.Then make a clock connecting to that command block.
6.Next, place a command block 4 blocks away (Remember this can be 4 blocks north or west or east or even south!)
7.Type in it:
/testfor @e[type=Arrow] {OnGround:0b}
8.And then, connect a clock to that to power it
9.Finally, get a bow and arrow and start shooting!You will see the shots are missiles (That's because it's iron man's missiles) if you want to, you can do this on a server and name the bow "Missile Shooter" and the arrow "Missile Ammo" it's your choice :) Enjoy!