I looked up a tool to make multiple commands occur in a single command block, and I found one, but it didn't seem to work in 1.8. So I decided to make my own. This is a simple tool that allows you to run many many commands in a single command block and they will all run in order. It also supports two separate methods for doing so.
Here's a video of making a single command block count to 50 using 50 /say commands using the two separate methods:
The two separate methods are important in different ways.
Mainly the first method, every command is executed at coordinates ~ ~1 ~ relative to the command block. But in the second method, every command is executed ~ ~1+n ~ relative to the command block where n is the command number it is on.
So using relative commands is difficult with the second method, although the second method is a bit faster and more reliable.
Here's a screenshot of the actual interface:
It's pretty simplistic. You just type in the list of commands, and click the button. Or check the check box to enable the second method.
That will create a little redstone circuit deep underground and out of sight. But it will make your arrows explode upon impact.
So just copy that into the program, make sure the checkbox is not checked, and click the button, then paste that into a command block and switch the block on with a lever and wait until all the minecarts go away and then go fire your bow.
Please post any issues you have with it so I can try and fix it.