I was digging through boxes looking for parts for some new cannons, and I stumbled across a small collection of cannon-design history. A bunch of old design iterations, before I reached the designs I use today. I figured someone or other might benefit from this brief stroll through memory lane. Here it is, the start of it all. This is an original-design BIC. Not my design, but certainly a huge inspiration. Well, almost. This one was actually a later prototype using a female-threaded breech. The original BIC was printed, then cut in half with my bandsaw so I could properly see the internals and take measurements. These babies were my first real success. Low-profile 50-round cannons, able to fire about as reliably and as powerfully as some non-printed cannons. These, installed in their 15-degree pivoting mount, saw action at my first NATS. The internal shape is similar to a BIC, but shortened significantly in the vertical axis. The O-ring breech was also copied from the BIC. Male threads on the breech, soldered onto a metal tube that gets glued into the cannon. I was never able to reliably glue the breech to the cannon, so I eventually moved to other designs. Well this is awkward. This was where I learned that 3d-printed parts are not necessarily pressure-tight. While my first-generation cannons could fire, it was not very hard. A lot of CO2 would leak out the bottom. Note how one of the cannons has been treated with acetone on the bottom, while the other hasn't even had the supports removed. Air leaking wasn't the only problem, however. The piston would sometimes jam in the up position, requiring a return to shore and a solid whack atop the turret to free it. Even when functioning correctly, they could only rapid-fire a few rounds at a time before failing to feed. Design Iterations. From top to bottom: A 50-round cannon using a 3d-printed female threaded breech, and a redesigned piston section that finally resolved the piston-jamming issue. The feed issue remained. Next, a 75-round cannon using the same geometry as the top. Same performance, same problems. But more rounds to shoot, so yay! Next, a hybrid experiment merging traditional brass fittings with a 3d-printed magazine. It functioned well, but was difficult to seal tight enough for a good, hard tweak. Also had feed issues. Last, a resin-printed 50-round cannon. I figured if I couldn't precisely control how specific layers got laid down, then I would print a cannon with such small layers that it wouldn't matter. This also proved that modern printing resins (ABS-like and similar) are easily strong enough to hold under pressure, at least for the rapid cycling pressures a cannon experiences. It also proved that the feeding issue was a geometry issue, not a printer problem. A pair of 3d-printed Deutschland sidemounts. These were the first sidemounts to go into my predreads. Like the BICs, these were not my design. It was remarkably compact, but demonstrated poor feeding characteristics. This was apparently a printer problem though, since the designer had excellent performance from the ones off his print bed. These cannons did see action at my first NATS. And here is all of the salvage from these cannons. Magazine screws, assorted o-rings and air fittings, pistons, and precious, precious springs. All the bits I cannot 3d print. And here is a batch of current-generation cannons getting assembled with acetone. I replaced the original predread sidemounts with my own designed coil cannons, and these proved stupendously reliable. Based on this clue, I started increasing the radius of the ammo ramp bends in my BIC-style cannons. Larger radii improved the feeding, until I found a combo that worked on every piece I pulled from the print bed. At that point, I went wild on the variations. 50-round BIC-style cannons, 75-round BIC-style cannons. Nesting designs that can stack together into twin, triple, or quadruple turrets. Offset or centerline barrels to achieve that perfect grouping. Coils with 50 or 75 rounds, and any desired barrel angle from level to 20 degrees down. The best part about BIC-style cannons is that they fit easily into a barbette. This example is a Lutzow/Scharnhorst barbette with three cannons in a pivotable mount. Two hours of brushing later, the cannons are assembled and airtight. But it's almost midnight and I'm out of acetone. I'll give them all a vapor bath tomorrow.
Looking good. Does this latest cartridge style cannon function well when off-camber? In my failed attempts with BICs (all the issues you highlighted) I always tried to keep the cannon body as perfectly vertical as possible and achieved gun-barrel down angle with a bent copper tube between breach and cannon body. Will this style cannon reliably fire when mounted at a down angle, since the breach is part of the printed assembly? In a boat like Bart, with B turret's dual sidemounts being mounted quite a ways off the deck, you need a decent amount of cannon down angle for those guns to be effective or you'll be shooting over the enemy next to you to hit the guy next to him. A turret is so close to the deck that you can't have much more than 5 deg of down angle, so I"m sure that wont be an issue.
I will test off-angle firing when I proof the cannons. I know it's possible, since I have a brass-and-copper cannon in my destroyer that literally pulls rounds up from the magazine using magnets and CO2, but all of my printed cannons so far have been installed vertically.
