/kill @e[type=arrow] it will kill the entity arrow so it doesn't keep spawning tnt and blowing it up a million of times it just blows up once then the arrow goes away.
Get Minecraft Explosive Arrows Pictures. Alternative way to make it: Add the possibility to craft explosive arrows in your survival world.
EXPLOSIVE ARROWS with 1 command in Minecraft [Link in ... from i.ytimg.com
Explosive arrows is a plugin, which let arrows and snowballs explode! Do you think that arrows are a little too weak for your taste? This project is inactive and its default file will likely not work with the most recent version of minecraft.
Alternative way to make it:
Currently not updated for minecraft 1.8! This is a minecraft tutorial on how to make arrows that are shot from a bow explode on contact. Exploding arrows could be added in minecraft. Explosive arrows | skript 1.8 1.3.
