How to Make a Gun in Minecraft
To easily make a gun in Minecraft, gather a dispenser, 3 redstone, 4 redstone torches, a lever, and arrows. Place your dispenser on the ground and a redstone dust behind it, with 2 blocks behind the redstone dust. Then, place a block above-left and above-right of your rear blocks, and place 4 total redstone torches on the sides of your bottom-rear blocks. Next, add redstone dust in the channel on top of your rear-bottom blocks, and place a lever on the back of the rearmost bottom block. Flip the lever to turn the gun on and fill it with arrows for ammo.
Gather your resources. You will need 6 blocks, 1 dispenser, 3 redstone, 4 redstone torches, a lever, and arrows. Place your dispenser, a redstone dust behind it, and 2 blocks behind that.  Place a block above-left and above-right of your rear blocks.  Place redstone torches on the sides of your bottom rear blocks (4 total).  Put redstone dust in the channel on top of your rear bottom blocks. It should start flashing. Place a lever on the back of the rearmost bottom block, and turn it on. This turns the machine "on", but stops the dispenser from firing. Fill your machine gun with ammo (either arrows or fire charges).  Prepare for war.  
Gather your resources. Place your dispenser, a redstone dust behind it, and 2 blocks behind that. Place a block above-left and above-right of your rear blocks. Place redstone torches on the sides of your bottom rear blocks (4 total). Put redstone dust in the channel on top of your rear bottom blocks. Place a lever on the back of the rearmost bottom block, and turn it on. Fill your machine gun with ammo (either arrows or fire charges). Prepare for war. 