The musket started as a concept before I joined SF as about my 4th piston cannon. This was up to that date my most advanced cannon. Since engineering is a hobby as well as a job, I looked at my past failures and looked to improve upon them. This is the result.
One of my old designs had a long piston, drilled holes for porting, and a dual diameter piston ( like a barrel sealer QDV ). The piston stuck, was slow, and if it worked flowed poorly. This is a successor to an earlier failure the Light Saber. A couple of SF members have been unfortunate enough to have seen it and it's super long piston.
For the design I wanted a compact cannon that would be easy to fill with a bike pump (before I got a compressor), flow very well, have a fast piston etc.
This meant a piston design. Due to the complexity of 2 o rings on the last cannon it was decided to try a build with no o rings on the piston. The goal was a very fast piston. Lightweight was part of the solution. The other part was a close piston ratio. A large seat and small outside diameter on the piston provided a close ratio piston. I did not have a drill press at this time. This build was completed with hand tools.
For the specifications;
The piston OD is 1.5 inch.
The valve seat is 1.25 inch.
The chamber is 2 inch PVC.
The barrel is 1 inch PVC
All PVC is schedule 40.
To keep the weight down on the piston, it was decided to attempt to move the weight of the barrel seal off the piston and move it to the end of the barrel. In doing so, the diameter of the valve seat became larger in diameter to make the piston ratio even closer to a 1:1 ratio.
To make the OD of the piston smaller in diameter, the piston was fitted inside a smaller piece of pipe. To reduce parts count and make it unique an unusual construction trick was done. I placed a 1.5 inch female adapter inside the 2 inch chamber by heating the chamber and shoving it in stretching the chamber larger to fit. The female adapter has a very short piece of 1.5 inch pipe inside it to become the piston cylinder.
The valve seat was created by hand with a small round file. I filed a groove around the outside of the barrel when it was much longer. This groove fit an o ring on the outside of the barrel. A ring was cut off a 1 inch pipe coupler and one end was carved out to fit over the o ring. The o ring was removed and the coupler was glued in place. Using the end of the coupler as a guide, the barrel was cut leaving this space for the o ring. the gap got a little bathroom caulk and the o ring was squished into the caulk. The barrel was stood on end and balanced to set the o ring in the glue true and flat.
To make a spacer to center the barrel. 3 short pieces of poly tubing was used. They were drilled sideways through the middle and these three pieces of tubing was zip tied to the barrel about 6 inches from the breech. The tubing squeezed down slightly to fit in the chamber and centered the barrel perfectly.
This launcher fit 1 inch gumballs and almost became the gumball gun. One day I killed a mouse (I hope I don't get banned for this) in a mousetrap. In disposing of it outside, I noticed it was about the right size. The mouse went over the back fence into the field beyond. The name stuck ever since. It has never been used to launch a live animal.
In testing to see if it met the design goals, a fast valve would be needed with good flow to get high speeds on light projectiles in the short barrel. I didn't have a chronograph. I decided to splat a gumball on a sheet of plywood to see if it would dent it. To my amazement, it punched a hole right through it.
The cannon was hard on valves. It broke 3 pistons. 2 broke in the center of the face of the piston. The 3rd broke on the side next to the eq hole. The 4th piston was made from HDPE. It didn't break. Unfortunately, the Musket got dropped and developed a crack in the front coupling. I retired it due to the leak and donated it to the Arlington HS science department.
Piston showing the small eq port and the crack that failed the last pipe cap valve. Most piston failures were a hole broken in the very center of the face of the piston. This is a spot not hit by anything. It is PVC fatigue that caused the failures. The hole was drilled with a printed circuit drill bit. It is tiny.
The PVC failures in this cannon was the direct inspiration to test alternate materials. This is the reason the ABS Cellular Core Test Cannon was built.
Edit; Added detail drawing of the barrel seal. The void behind the o ring is filled with caulk.
