This is my most powerful, most advanced spudgun that I have created yet.  It uses a piston/diaphragm technology that is explained below.  I give credit to IOD Air Cannons for its help in solving a couple of my problems.  Iin the testing phase with this cannon now but it should be completed soon.

This is the outer casing of the Howitzer.  What is seen here is the actual size of the gun when it is completed.   Nothing at this stage has actually been glued.

By now you are probably wondering exactly how this thing operates since the valve is in the rear and the barrel is inside the chamber.  Looking at the diagrams below you can see that the barrel reaches inside the chamber almost to the back.  Between the back and the barrel there is a sliding piece of device called a piston.  The piston acts a an air tight seal. 

When the chamber is charged (with air) the piston slides forward pressing its neoprene seal against the barrel (Figure B).  The air then seeps around the piston and fills the area on the outside of the barrel towards the front of the gun (Figure C).  A projectile is loaded then the valve on the rear is released. The area behind the piston is instantly depressurized causing the high pressure zone in the front of the gun around the barrel to surge towards the low pressure zone (the area that was just depressurized).  Next this air slams the piston into the back of the gun with tremendous force.  The piston then acts again as a seal and the air is left with no where to go except through the barrel (Figure D).  Basically this is like having an instant opening 2" Solenoid valve in the standard chamber/valve/barrel assembly which all adds together to deliver a projectile immense distances.  Some of these guns have been said to shoot up to and over one mile with specially engineered projectiles.

The piston is nearly completed but I don't have any pictures yet.  They will be coming soon. The piston is constructed out of a 3" PVC coupling with 2 steel disks in it.  A thin layer of neoprene is then attached to the top and is used as the diaphragm.  The neoprene is rated at 1000PSI+ so it's pretty good stuff.

A 1" in-line solenoid valve is used for the pressure relief valve.  Shown in the middle is the valve assembly head.  Located there is the solenoid valve, pressure gauge, and the Schrader valve.  On the right the bumpers are pictured.  The bumpers are small circular vinyl tubes that have been installed to protect the piston when it slams back towards the rear of the gun when firing.

This is most certainly not the type of cannon that it would be OK to ram the projectile down too far into the barrel since it would take ages to unscrew everything and recover it.  That is why I have put in a bolt, cased with a coupling to ensure its air seal.  This prevents a projectile from sliding into the air chamber.

No really,  I am not that small.