1/9 scale 8" Chambered Shell Gun of 63cwt

The 8" chambered shell gun of 63cwt was introduced in 1840 to arm the gun deck of first class frigates and ships of the line. There were four patterns made, although there are no drawings or surviving cannons of the first pattern. I was drawn to the second pattern for its harder to fabricate cascabel and generally older style. Originally these were cast so it was easy to get nice flowing shapes, but much harder with a manual lathe and mill. I ended up roughing it in with machinery and finishing it with a die grinder. The third and fourth pattern used a more typical knob shaped cascabel which would have been easier to machine. The USS Cairo was armed with three guns of the third pattern.

I've found very few period photos of these guns, although I believe this might be an 8" shell gun at Fort Fisher. Certain models of 32 pounder and 10" shell guns of 86cwt have the same profile, so it's pretty hard to say for certain that this is an 8" without knowing the length. But this is the overall appearance I'll be aiming for.

First I started with a 14" long chunk of 2.75" 1018 and turned it down to just over 2.5". Then I drilled a 7/8" hole all the way through. I'll ream it out to size later.

Next I bored a ~3.5º taper to the bore at the muzzle. This was done on cannons of this era to make loading a bit easier. On the original, the bore was 8.5" at the muzzle. Then I flipped it around and bored out a counterbore for the breech plug to seat against.

Then I laid out where the different diameters started and turned the sections to size.

Then I turned the tapers.

Next it was over to the mill. I put Dykem on the muzzle and scribed a line across the diameter so I can index the trunnions 180º.

Then I cut a 1" diameter pocket for the trunnions. This end mill isn't center cutting so I had to cut a pilot hole first.

Next I made some ~.0015" oversize trunnions.

Then I pressed them in. I'm not entirely sure about how strong these are. I was considering drilling a hole on the underside of the gun and pressing a cross pin in to prevent them from coming out... or possibly a dab of weld. But this gun isn't going to get shot much so I think I'll just measure across the trunnions and fix it if it becomes a problem.

With the trunnions installed I could ream the bore. I wanted to make sure I removed any deformation in the bore from pressing the trunnions in. To be completely scale, this gun should have a bore of .889". But I want to be able to shoot 7/8" projectiles, so I reamed it to 1/40 over, or .897". I made the breech plug .002" bigger than the counterbore it seats against.

Then I used an oxy acetylene torch to shrink fit it in. I put it back in the lathe and cut a V groove weld prep. If I were smarter I would have done these grooves before shrink fitting...

There it is welded up. It was still surprisingly concentric. Maybe .0005" at the biggest diameter.

Next I removed the excess weld and turned the ring at the base of the cascabel and the dome on the breech.

Then I build up some weld for the vent field and the stiffeners.

I put it back in the lathe and roughed out the profile of the stiffeners and turned down the diameter and size of the vent field.

Then I took it over to the mill and took the stiffeners and vent field down to the correct width.

I used a countersink to give the front edge of the vent field the slope.

Real machinists look away! I've cut off the extra cascabel and spent an eternity with a die grinder getting the stiffeners looking closer to what I see in the historical photo.

This is the best setup I could cobble together to cut the notch for the breeching. Throughout the project I made sure my scribe lines on the muzzle didn't get worn off so I could set this up.

The stiffeners are a little rough and there are a few pits around the ring where the weld wasn't quite enough, but I'm pretty proud of sculpting that glob of weld down to something this close.

So that's pretty much the barrel complete. I'm going to make a 4 truck naval carriage for it next and will update this page when it's done.