How to make a halberdier TNT mortar (1.8.1)

1.put 3 dispensers in a row with a 1 block gap between them

2.put slabs around the dispenser (if you dont have TMI) and put waters on them

3.put more dispensers 1 block higher than the watered dispensers(wich is not a word xD) and 1 block away from the gaps

4.put a lever on the ground somewhere that connects to the 3 watered dispensers with redstone wire

5. also same as the unwatered dispensers (lol)

6.put tnts in the dispensers

THERE IT IS NOW LETS END THE WORLD LIKE A BOSS XD