It may be a simple design but it's still fun to use nonetheless.
Note that using more than one dynamite might slow down the spear.
The Chamber is where you put the gunpowder (or dynamite in this case) which will propel your spear.
You will want to have a little hole infront of it to let the spear in.
If you make it large like this you can even fit an Atom bomb in it, but most of the time you will only need a single dynamite.
If you feel like it you can also move it's back so the dynamite won't move when you angle the thing like this:
The barrel is where you will put your projectile (in this case a spear).
I made mine out of 4 long beams which is working out well imo.
Place down the dynamite and Spear, if you built it right the spear should be able to slide through the barrel and into the chamber.
Connect the dynamites to a button.
Now instead of following the spear you can get to press a button from where you aimed it at and wait for it to come to you instead. It's harder to hit but it's worth it if it goes well.