This is the first shoulder held spud gun that I have built.  It is also my second most powerful one and demands a great respect for safety.  Before I started this project, I thought to myself what would happen if I could double the air flow using 2 valves?  It would tremendously increase range and muzzle velocity at any rate.  The general idea for this cannon came from IOD Air Cannons. So I hacked and stuffed and glued and all the rest of it 'til this monster was born.  It'll punch a PVC Dart pretty muchly out of sight. That is pointing the muzzle almost straight up.  The real force comes from a nearly 300 cubic inch air chamber positioned in the standard over-under style.  This air cannon is pressurized just short of my sniper, which means if you think about it, this cannon is exceedingly more powerful.  
 

This Air Cannon needed minimal drag, so I greatly reduced the drag using a 45 deg. elbow rather than a 90 deg. elbow.The electrical configuration is very different compared to my sniper rifle. The 3 9 volt batteries simply weren't enough to get these 2 valves open.  So I used 4 6-volt lantern batteries wired to a self designed foot activation pedal. Why did I use a lower voltage?  The lantern batteries have a much higher capacity.  The valves in this setup had to be wired in series to perform simultaneously. The arming configuration is the same as my rifle.  There is a toggle switch and momentary switch. Just in different places.

Inside the box...                                             Foot Activation Pedal

While building this cannon I had no idea what the recoil would be like.  I figured that it probably wouldn't be a good idea to simply put a switch on the main gun.  I thought that pushing a switch on the gun would put me slightly off balance and I wouldn't be holding the gun with full strength.  The foot pedal allows me to brace the gun properly and to simply slam my foot down for the release. 

Also, I used banana plugs for a quick disconnect system from my electrical components.

The pedal is soon to be done away with due to my recent success with the trigger valve system.  This will allow the cannon to be fired by simply depressing a switch.  This system will make the cannon much more portable and give it a quicker release time by simply depressing a valve.  You can check out the design on the trigger valve page.