Supplies:
-1 dispenser
-9 redstone dust
-8 placeable blocks, (not something that can be activated by redstone ex: tnt)
-7 redstone torches
-1 lever (or other switch)
Space:
5 width x 10 length x 2 height
Firstly, the black wool indicates the space that is needed in rectangular form, you could make this smaller. Secondly, all of the blocks you need to place are blue wool.
Step 1:
Get supplies.

Step 2:
Place dispenser in the front row, in the middle.

Step 3:
Place 1 redstone dust behind the dispenser.

Step 4:
Place three blocks as shown.

NOTE: This is taken when standing on top of the dispenser.
Step 5:
Place 1 redstone dust in the center block.

Step 6:
Place 2 torches beside the redstone.

Step 7:
Place 1 lever on the left block with a torch, this is the trigger. (In background is another gun)

Step 8:
Place one redstone dust behind the other torch block.

Step 9:
Place one block on a diagonal with the redstone just place, and put one torch on that block to activate the redstone.

Step 10:
Place another redstone dust, another block, and another torch.

Step 11:
Do the same, but in a different place and in a line with the previous torch.

Step 12:
Place redstone to go around the corner.

Step 13:
Place another block with another torch.

Step 14:
Place a redstone so that it is beside the previous torch, and attached to this new block.

Step 15:
Place a redstone torch and a redstone dust connecting to the block in "Step 9". If you have done this correctly, you will notice that the torches start flashing.

Step 16:
Flick the switch to activate machine gun (do not forget to load the dispenser).

NOTE: In this picture, the switch is not activated, and the gun is not shooting.
IF YOU HAVE DONE THE WHOLE CIRCUITRY CORRECTLY IT SHOULD LOOK LIKE THIS:

Hope this helps!
{SMILIES_PATH}/flintnsteel.png












