Making a 14th century Hand Gonne

Last Fall I taught a day-long workshop on “Primitive Black Powder Firearms” for the Liberal Gun Club‘s Annual Meeting in Las Vegas. In addition to my own black powder guns, I borrowed a couple of items from friends to help fill out the historical selection, including this very nice reproduction of a 14th century .62 cal cast bronze hand gonne:

I had shot the gun previously with friends, and it never fails to put a smile on people’s faces. It’s so simple: pour gunpowder down the muzzle, roll in a lead ball (tolerances for these guns are very slack, and the ball will roll right back out if you’re not careful), add a little powder to the touch-hole on the top, and light it off when ready. Very basic. Very fun. People in the workshop loved it.

And I decided that I wanted to get one of these for my own collection.

The problem is, they’re almost impossible to find. I spent a couple of months poking around online, asking friends, and the closest I could come were a couple of simple hand gonnes made using steel. Nice, but not what I was looking for.

So I started to think about making my own, and I consulted with an old friend who does bronze casting for his jewelry business. Turned out that it was certainly possible to do such a project, but it was bigger than my friend’s casting set-up could handle. We set aside the idea for the time being.

But I thought some more about it, and figured that such a bronze hand gonne was so simple, that it should be possible to make one without casting. I could order a bar of the appropriate alloy of bronze, have a machine shop bore it out, and do the external work myself. I tried contacting some local machine shops, explained what I wanted done. Most never responded. The ones that did had no interest in the project. I was stymied again.

By then, however, I was invested in the project. Again, I thought through just how basic the hand gonne was, and I figured that if I ordered the correct components, I would be able to make one without a machine shop. In fact, as I thought it through, I realized that it would be possible to make one just using some very basic modern tools which almost anyone would have or could get at a modest price. So I set out to do just that.

And this is the result.

Now, before we go any further, let’s get a few important caveats in place:

• This is a description of how I made a black powder hand gonne for my own use
• I am not recommending that you make a black powder hand gonne
• If you do decide to make a black powder hand gonne, I am not recommending that you make it this way
• Any black powder hand gonne is potentially dangerous, and if you make one, the risk is entirely on you
• A black powder hand gonne is a firearm, and all the rules of safe handling and usage of a firearm apply

OK, we clear about that? Good.

The tools and materials needed.

So, in thinking it through, I decided that the most basic tools needed for this project would be:

• Electric drill with a 1/2″ chuck, misc drill bits
• Hacksaw
• Basic hammer
• Hand sledgehammer or small anvil
• Clamps or vise
• Metal files
• Metal chisel (‘cold chisel’, 1/2″ wide or so)
• Measuring tape/yardstick/square or similar
• Calipers

Now, some additional tools that are common, and which I used to speed up the whole process:

• Belt sander
• Bench grinder
• Dremel or similar rotary tool with various small bits
• Side-cutting pliers

Pretty basic, right? So is the list of materials needed:

• Bronze stock
• Sandpaper (various grades, starting with 60grit)
• 1/2″ iron bar stock
• 3″ common nails (x2)
• Epoxy
• Duct or box tape
• 1.75″ x 48″ hardwood dowel for the stock
• Stain/finish for the stock, if desired

In addition, I used a number of bits of scrap wood, foam, and wood screws I had in my workshop. You’ll see.

Selecting the bronze stock to use.

I knew that historically, early black powder guns were typically constructed of a type of bronze called gunmetal or red brass. This is a bronze alloy containing mostly copper, some tin and lead, and a little zinc. I spent some time looking over modern bronze alloys which were readily available, and settled on “Bearing Bronze 932” as being a reasonable approximation of common gunmetal.

The modern metal industry offers a range of different types of products. What I figured was that I could get a product called “hollowbar”, which is basically a thick-walled pipe. That would allow me to select both the overall diameter and the wall thickness. By choosing a 1.75″ O.D. hollowbar with a 0.625″ I.D., I would get a suitable length of bronze which didn’t need to have a bore drilled into it. In addition, I ordered a length of round bar stock with a nominal 0.625″ O.D. that I could use as a breech plug. Metal prices fluctuate regularly, but I was able to get both pieces shipped for about $160.

Both pieces of bronze arrived. As expected, they were “overcast” — meaning that they were slightly larger than the specs given. The hollowbar was 13″ long, and the bore down the center of it was at 0.585″. The round bar stock was likewise 13″, and the O.D. was 0.675″. That meant that I would need to ream out the bore to .62 cal and shave down the bar to fit the finished diameter of the breech.

Reaming out the bore.

I didn’t order a solid length of bar stock because that would have required that I have the ability to drill out the bore. Even making a smooth-bore hand gonne (with no rifling) would present a substantial technological challenge which would have required, at a minimum, a floor-mounted drill press if not an actual metal lathe.

However, by ordering the hollowbar, I would already have the basic geometry of the hand gonne provided. The hole down the center would already be established. It would just be a matter of getting the bore to the correct diameter to handle a .62 cal lead ball.

To do this, I decided that the best approach would be to use a length of 1/2″ iron rod (called a mandrel) with a piece of sandpaper at the end, driven by the hand drill. It would take time, and require frequent changes of the sandpaper, but it would give me the ability to ream out the bore with a reasonable amount of control.

This is easy to do. You just use one piece of tape applied to the back of your piece of sandpaper, with a tab of about an inch protruding past the edge of the paper. Then you apply another piece of tape to the tab, and use the overhang to secure it to the mandrel. Like so:

The next thing I needed to do is secure the hollowbar stock so that I could spend time reaming out the bore without the stock moving. I decided to make a simple sandwich of scrap wood, dense foam, and screws to hold everything in place:

Then it was just a matter of reaming out the bore slowly, frequently stopping to change the sandpaper, dump out the waste material, check the progress, and let both the drill and the hollowbar cool down. It took a total of about 8 hours over four days to do this.

But, in the end, a .62 cal lead ball would pass freely through the length of the hollowbar:

Now, one thing I want to note: when you repeatedly insert a mandrel with sandpaper from one end, that end will tend to get over-reamed. So I was careful to consistently do this from the end of the hollowbar that I intended to be where it would be mounted to the wood stock later (i.e.; not the muzzle end).

Making the socket.

The hand gonne would need to be mounted to a stock of some kind. Historically, these seem to have been just a simple stave of wood, with the hand gonne stuck on the end. That was also the style of the others I’d seen in person, so it was what I decided to do.

There were a number of ways that such mounting could be accomplished. I considered the options and settled on just creating a hollow at the end of hand gonne that would accept about a 2″ deep piece of the stock.

Therefore, to make the socket, I needed to remove additional material to a depth of about 2″. To do this, I used a drill with a 5/32″ bit (marked with tape to a 2″ depth) to create a starting set of holes in a circle:

Then I went to a 1/4″ bit to remove more of the bulk:

After this, I used the cold chisel to start to cut through the remaining material:

And then the Dremel rotary tool with a steel carving tip to remove the rest of the bulk and thin down the sides some:

I wasn’t worried about it being perfectly symmetrical or smooth at the bottom, since these areas would be hidden by the stock.

Making and installing the breech plug.

Since I was starting with a length of hollowbar, which had a hole down the center of the entire length, I needed to close up and secure the breech of the gun. The historic models and modern versions which are cast just have a closed-off breech to start with, so this step isn’t necessary.

Black powder is a low-pressure propellant, and I could have probably just gotten away with inserting a tight plug of bronze and then mounting the hand gonne to the stock. But I wanted something that would be more secure. More secure, yet still low tech (no brazing or anything). I decided that a couple of mild steel rivets through the outside of the hand gonne, and through the plug to the other side, would be sufficient. But this meant that the plug would need to be long enough put a couple of rivets through. I settled on a 2″ plug.

Using the calipers, I checked the bronze rod, and confirmed that it was larger than what I wanted. I also checked by trying to insert the end into the breech end of the hand gonne, just to be safe. It was still 0.675″, so I needed to file/sand it down:

Checking frequently, I continued that until the rod would barely start to insert into the breech. Then, using the hacksaw, I cut off a 2″ long piece of it:

I did some additional sanding, then inserted it, first by hand, then using the hammer and the iron rod I’d used as a mandrel to ream out the bore:

Shaping the outside.

OK, first things first: at this point, you could rivet the breech plug in place, drill the touch-hole, mount the hand gonne, and use it. The shaping I’m about to show/discuss is not necessary to having a functional black powder firearm.

But the historical record shows that most of these were shaped and/or decorated in some fashion. Likewise most of the reproductions I’ve seen. I decided to do something similar to the design of the one my friend owns, though going with an octagon form rather than a hexagon one.

Why bother? Mostly just for aesthetic reasons. But also, the entire bulk of the hollowbar isn’t necessary for the hand gonne to be strong enough to function. You do want to have some extra bulk/strength to contain the primary explosion of the black powder, in the area that is called the “chamber”. But as the lead ball/bullet starts to move down the barrel, the pressure drops off quickly. Meaning that the barrel walls don’t need to be quite so thick/strong. By removing the excess, you can cut down on the weight of the hand gonne by about a third. I also decided that I liked the flare at the muzzle often seen on these guns, and thought it would help connect it visually to that history.

Since the final shape of the hand gonne is largely an aesthetic decision, what follows is just a quick photo-essay of the steps I took to come up with my preferred design. Also, while I started out using a file, I almost immediately shifted over to using a belt sander to get the overall shape, then a bench grinder to rough out the barrel, followed by more use of the belt sander. Basic shaping was done using a 60grit belt, then finished with a 150grit belt.

First, I marked the end of the muzzle with the basic shape I wanted:

Then I put it back into the trough to hold it in place:

I chose an octagon shape for a simple reason: it would be easier to keep it aligned in the trough while working.

Once the overall shape was defined, I started to cut down the barrel bulk:

This all actually went faster than I expected, just a couple hours work with the belt sander & grinder, with frequent stops to check dimensions with the calipers.

Securing the breech plug and drilling the touch hole.

Once I had the exterior shape mostly finished, it was time to secure the breech plug with a couple of mild steel rivets and drill the touch-hole (how you fire the hand gonne).

The first step was to carefully measure and mark the locations of the rivets and the touch-hole. I did this by using a dowel from both the back of the socket and from the muzzle. I wanted the rivets to be evenly spaced about 1/3 the way from the front and the back of the breech plug, and the touch-hole to be positioned so that it was just in front of the breech plug.

Using a Sharpie, I marked the location of each of the holes. First I used a 7/64″ bit and drilled the touch hole, centered on that face of the octagon and angling slightly back into the chamber for the black powder. This would tend to force the jet of hot gas forward away from the shooter when the gonne was fired. I used a larger drill bit to start a larger hole just on the surface — the beginning of a simple ‘pan’ to hold a small amount of black powder.

Then I selected a drill bit the same diameter of the 3″ nails I was going to use for the rivets, and drilled through the exterior of the hand gonne, the breech plug, and out the other side of the hand gonne:

Next I used the Dremel tool with a small grinding head to deepen the ‘pan’ and slightly counter-sink the holes for the rivets. I cut off the head of the nails, and inserted them through the holes, cutting them off with about a 1/8″ protruding from either side. Then these were hammered (with a hand sledge under them, though if you have an anvil that will work better) so that the mild steel filled the counter-sunk area:

Next I dressed those areas again using the belt sander and 150grit paper:

Shaping and mounting the stock.

I’d hoped to find a suitable length of oak, ash, or hickory to use as the stock. I settled for a 1.75″ x 48″ poplar dowel I was able to select at a local lumbar yard.

The first thing was to shape the end to fit the socket:

Once I had it so that it fit, I needed to secure it. I decided that normal 5-minute epoxy would be sufficient for this purpose. So I did some additional undercutting of both the dowel and the socket walls (so that the epoxy would fill in those, and couldn’t just pull loose). Then I mixed the epoxy, poured it into the socket, and shoved the dowel into place. To hold everything in place for the 24 hours needed to let the epoxy cure, I used this high-tech set up:

Surprisingly, this worked, and the dowel rod was almost perfectly straight off the back of the hand gonne.

I had debated whether or not to leave the dowel round, or to put partial flats on it, or what. But once the epoxy had set, the round dowel just didn’t feel right, so I decided to go ahead and use the belt sander to shape the dowel into the same shape/dimensions as the hand gonne:

If you look carefully, you can see the slight skew of the hand gonne off to the left. It’s only 3 or 4 degrees, and really isn’t noticeable when you actually hold the thing, but it is there. I decided not to worry about it.

I wanted to have some basic surface protection for the stock, so used some dark walnut colored Danish Wood Oil I had available:

Proofing the hand gonne.

The usual recommended procedure to test a home-made black powder firearm for safety is to take it to the range, put a double load of powder into it with a lead ball, secure the firearm, and then fire it from a safe distance using a string or fuse or whatever is necessary. I’d ordered in some cannon fuse for just this purpose.

I got out to my range on a cool Friday morning, when I was reasonably sure that no one else would be there. I wanted to avoid putting anyone else at risk, on the off chance that my project didn’t work out and wasn’t safe. That is, if the thing blew up, I wanted everyone else to be clear.

I set up a large sheet of cardboard (about 2×4′), about 7 yards from the gonne. I put in 120gr of FFg black powder, twice the standard load I’ll shoot out of the thing, along with a .62cal lead ball (345gr). I then laid the gonne down on a picnic table, with a fold piece of cloth under the muzzle end to maintain a slight elevation. Then I positioned my black powder range box (minus the black powder casks) balancing on the stock just behind the gonne as a protective barrier. I positioned my usual range bag on the back of the stock to help hold it in place. And I set up an inexpensive mirror and my smart phone so the phone was protected but would record the first firing of the gonne. Like this:

I cut a 6″ length of cannon fuse, inserted it into the touch-hole. I started the camera recording, then lit the fuse. Then got about 10 yards away, on the other side of my vehicle. And this is what happened:

And here the relevant bit is in slow-motion (1/8th normal speed):

Mwahahahahaha! It works!!!

Here’s where the first shot hit:

Not bad! It was time for the second shot, using a normal charge of 60gr of FFg black powder:

I was stabilizing the gonne with one hand, while filming with the other. There was a decent amount of recoil, even with the standard charge.

I went ahead and shot it a third time, again with a normal charge, but this time holding it and shooting it as I normally would. Again, I noticed a fair amount of recoil, even given the substantial weight of the whole thing (I’d guess ~10 pounds or so). But it’s not the sort of thing that most people would mind at all.

And all three shots hit in roughly the same place at 7 yards:

Not bad.

Given the very basic design of this thing, it’s still respectable in terms of control and power. I didn’t chrono it, but based on previously checking black powder guns, I’d guess that the .62 ball was probably traveling about 800fps. That gives a muzzle energy of about 500 ft/lbs, or about what a modern .40S&W handgun would get with typical loads. In other words, it’s an effective weapon, at least at moderate range. Not bad for a technology that is almost 700 years old.

Conclusions.

To repeat myself from the start:

• This is a description of how I made a black powder hand gonne for my own use
• I am not recommending that you make a black powder hand gonne
• If you do decide to make a black powder hand gonne, I am not recommending that you make it this way
• Any black powder hand gonne is potentially dangerous, and if you make one, the risk is entirely on you
• A black powder hand gonne is a firearm, and all the rules of safe handling and usage of a firearm apply

But, after the ‘proof’ shot, I did a close inspection of the hand gonne. There were no signs that anything had shifted or been stressed. Same thing after the two subsequent ‘normal’ charges were shot. So my conclusion is that the gonne is safe, though of course I will keep a close eye on it going forward.

And overall, I’d have to say that the project was a success. It is possible for an average person, using common, non-specialized tools and a little ingenuity, to make their own reproduction 14th century hand gonne with modern materials. My total cost out-of-pocket for this project was under $250, and now I have a couple new tools as well as the gonne.

Thanks for coming along for the ride. Feel free to share.

Jim Downey