This article details how to build a single shot piston interrupt cannon which is typically found in the Queens Own club.  It consists of a brass body...

a steel brake line (or brass tube) magazine, a brass piston interrupter, and an O-ring with a ¼" compression nut (the kind used on plumbing fittings).  The O-ring holds the barrel into the cannon by the compression forces exerted by the compression nut; it will not allow the barrel to fly out when the gun is fired.  The weight of the gun can be entirely supported by the barrel after the compression nut is properly tightened down.

Fabricating The Breeches  

1.      Cut the 1/2" brass hexagonal stock to a length of 1.35".  chuck the hex up in the lathe, turn one down to .425" over a length of .35"; using a 7/16" - 24 tap, cut the threads for the o-ring compression nut. 

2.      Clamp the stock in a vise with a 1/2" block under the barrel side to achieve the 10 to 15° (up to 20° works) angle for the magazine feed, and mill (or drill) a ¼" diameter flat bottom hole 3/16" deep (3/16" is measured from when the flat bottom mill touches the breach). 

3.      Solder a 3/4" long piece of ¼" diameter brake tube in the hole (or use some brass tubing).  Use enough solder to completely fill the bottom of the hole.  Be sure to really sand the tubing clean with emery cloth for a good solder joint.

4.      Chuck up the breech in the lathe with the magazine pointing towards the tailstock (see image below) and drill it full length with a #23 (.154") drill bit (slightly smaller/larger is ok also, since it's a pilot hole).

   
5.      Bore out the magazine tube (see image below) with a hand drill and a #11 (.191") drill bit, while being careful not to drill into the opposite wall of the breech too much.  If you take the corners off of the flutes on the drill bit, it won't grab so bad when it's breaking through to the centerline hole you drilled in step 4.
 

6.      Drill the breech full length with a #16 (.177") drill bit. 

7.      Drill to slightly below the middle of the magazine with a #11 (.191") drill bit (so it intersects the #11 drill job for the loading tube).  This will allow the bearing to go from the magazine up into the barrel.  Next, drill the pocket for the barrel to a depth of 3/8" with a 1/4" bit.  

8.      Turn it around (magazine now faces the chuck)& set the compound feed to approximately 87°, cut the taper & cut the threads for fitting into the MJV-3 Clippard valve (1/8" national pipe threads).  Use a pipe tap to cut the threads, can't see taking the time to single-point it on a lathe. 

9.      Drill to a depth of 1/2" with a "N" (.302") drill bit ("M" is OK also).  This is the space where the piston will ride up and down, keeping the gun from firing doubles by blocking off the magazine. 

Cutting the Piston

1.      Chuck up 5/16" brass stock, leaving about 1-1/4" sticking out.

2.      Face off the end & drill to a depth of 13/16" with a # 35 (.110") drill bit.

3.      Turn the stock down to a diameter of 0.29" (if it is undersized by .005" or so, it will still operated smoothly) for a length of .8".

4.      Turn the piston down over the forward .1/4" to a diameter of 0.170".

5.      Using a cut-off tool, measure for the finished major diameter length of 0.55" and cut down to about ½ diameter.  Take a file & round over the corners, then complete making the cut-off.

6.     Place the piston in the breech, screw it into a Clipper MJV-3 valve, & adjust the piston by cutting (or filing) the top down so the bearings will just roll above it into the breech.  I have found that chucking up the piston in the lathe (or in a drill if you are out at the pond), and lightly hitting it with a file works great.

Adding Rotation

1.      In order to rotate the barrel without hacking the servo, a pulley of approximately .45 to .5" ID was soldered to the steel brakeline barrel.  I would have preferred stainless steel, however, lead solder will not adhere to it.  I apologize for not having written down the exact diameter of the pulley, I would have liked to have had that number available for you.

2.      The grooves of the pulley were purposely made deep, to allow the business end of a 90 degree keeper to ride in the groove with the other end screwed to the breech.  The keeper prevents the barrel from being blown out of the breech when the weapon fires.  Unfortunately, the keeper is not visible as it's on the opposite side of the gun from where this picture was taken.

3.      The cable is nylon covered stainless steel fishing lead, each end is terminated in a stainless steel electrical eyelet that is screwed to the servo arms with stainless screws.  To keep the cable from slipping on the barrel pulley, two small diameter holes were drilled in the upper lip of the pulley; the wire was looped around the pulley a couple of times, shoved up through one hole & down through another and wrapped around the pulley again.  A drop of CA on each hole/cable interface & the cable would not slip.  The eyelets were than compressed onto the cable & screwed to the servo.

4.      Paul had a great idea for depression on this style gun, due to space limitations, it was impossible to fit a servo for this purpose.  However by bending the barrel at less than a  90 degree angle, the gun itself was mounted at an angle so that over the stern the barrel was parallel to the deck.  With a little adjusting to the gun angle, the gun would fire into the water at about 10' behind the ship.  Here's the beauty part: when rotated athwartships, the barrel was now aimed down for some good waterline shots because the barrel was bent less than 90 degrees.  Very cool.

5.      The servo is mounted in a CNC machined aluminum fitting and the accumulator is used to tension the rotation cable.  That's about all I can remember of note on this gun, hope it helps.  I unfortunately got rid of the boat & the gun several years ago.