All, I am using a post rather than the resources simply to add additional files and explain the purpose of each a bit. The intent is to provide an architecture that enables anyone with a modicum of CAD knowledge to easily create a functional cannon using a 3d printer. I am providing STEP files so that people can tweak as necessary to fit their specific spring/pistons. Pistons should be 0.61 OVERALL length, .060 flange thickness, 0.175-0.180 Diameter, 0.315 flange diameter. Standard caveats apply, you are responsible for your own testing and printer setup. Printer setups, infil, and material vary greatly, resulting in significant differences in inherent strength of the finished cannon. I can not and do not attempt to account for all possible ways that one can mess up a print. I generally print ABS or PLA, 4+ Walls, 50-75% cubic infill, with 1 halving of the infill 3mm away from anything of importance. I use ONLY 3D850 or 3D870 PLA or ABS from filastruder. I have noticed that 3d870 from filastruder prints at cheap abs temperatures (220C or so), and their ABS on mine prints at 250C (vs 220C for other cheap ABS I have used) Caveat Emptor The cannons themselves have the selector at the breech. The twin designs all require magnets to function (buy neodymium, ND40+). Make sure to armor any exposed magnets lest a lucky shot destroy them and disable cannons. The breech plug is sealed once set using E6000 or any other popular gummy adhesive. High flow solenoid use is required. Most testing done on strike solenoids or spartan solenoids. strike's fire faster IMHO for me, but it could just as easily be the switch board. O ring required is size -106 Shore A 70 durometer. I use buna. for twins use matched bag O-rings (e.g. take two from the same bag, replace in pairs) Now onto the fun stuff. First off the 1U twin: Used successfully in Provence, extensive bench testing, based on duca design. The solid file is for the french battleship provence Can be easily modified to other turrets Shows manual supports, can remove and add your own The CORE file is the gas domain, containing two alternate fill ports. either use cad to plug one of the fill ports for each barrel or plug with 1/4-20 setscrew CORE has magnet positions outside the barrels, suggest putting between if you want to (see Province example CORE has 1/4NPT threaded inlet CORE has spherical joints between the barrel thread domain and the rest of the cannon, which enables one in CAD to easily set the down angle UP TO ~15 degrees, NO MORE CORE requires you to add your own overhang cutouts if necessary, the provence example shows some I use Adjust diameter down to match piston after boolean subtraction (see red below). In general this is true of all of the CORE files in this post Second, the 0.5U twins for the duca: Used extensively in Duca. Took duca from Meh to one heck of a fun ship. The solid file is a finished duca set of twins. Inlet is a glued/shrunk fit and staked copper tube (1/4in OD) The CORE file contains gas passage. same caveats as above apply, however, inlet must be designed in yourself to fit your specific geometry. The third is the 1U sidemount. This one DOES NOT REQUIRE magnets. This is the original of all the cannons, used extensively in provence and inspired the entire family. Solid File shows example turret for french bb provence No magnets required Life rafts are structural CORE file shows the gas domain, same caveats as the first (1U twins) core file apply I have a prototype 1.5U sidemount gas passage designed, have not had time to test it. it will come in a reply to this post. I have not really put much thought into tripples (don't have anything that will run with them) but with two solenoids, it should be trivial to expand the twins into a set of tripples. This is next on my design list once the 1.5U sidemounts are complete.