Weird Pressure Question

[Panzerschwein]

Hello all! Now this is a weird one, even for me to ask!

I am trying to commission someone to build me a replica of a 14th century bronze handgonne (hand cannon). If you click "Medieval European Handgonne #1" HERE you will see the .55 caliber original bronze specimen I am trying to have recreated for me. I am going to have it made in .540" caliber so I can use .54 cal balls and patches that I already have plenty of. This specimen seems to have a thick barrel, as most handgonnes do, and tapers to the end. The breech should be something like an inch and a half wide, and the muzzle looks to be about an inch wide with .55 bore.

So, assume we are using a traditional bronze of 88% copper and 12% tin, and I was using 230 grain .535" lead round balls with a thin patch, and maybe up to 40 grains of FFG black powder, and a simple bronze barrel of the dimensions shown in these pictures, how safe do you think that would be? What kind of pressures would said load produce?

I have seen people make reproduction handgonnes in brass and fire them, so I am curious. Of course I could always just have one made from steel, but I would love to have an authentic one made of bronze.

So what do you guys think? Will this be safe provided I don't overload it? Thanks!

 

[Jim K]

No way I would answer that question, or suggest anyone else do so. If I say it would be safe, and you find that your headache is being caused by that piece of bronze sticking out of your eyeball, you could sue me for a zillion bucks.

Jim

 

[Curator]

Cooldill:
Not all "Bronze" alloys are suitable for gun making. However you are going in the right direction. This is what you will find by googling "gunmetal bronze:
"Gunmetal, also known as red brass in the United States, is a type of bronze – an alloy of copper (85%), tin (5%), zinc (5%) and lead (5%).[2] Originally used chiefly for making guns."

Gunmetal bronze alloy was the preferred metal for making cannons right up to the ACW/WBS 1865 or so because of its corrosion resistance and resilience. Unlike cast-iron, bronze cannons would swell or bulge before they burst so were considered safer.

Your proposed load does not seem excessive for a properly made hand-cannon.

 

[Patocazador]

I have no clue when it comes to bronze but as with other metals, a forged barrel would be safer than a cast barrel. Castings tend to have hidden flaws that could cause unforeseen problems.

 

[Mike OTDP]

It's my understanding that most of the "bronze" firearms and cannon were actually of brass.

 

[Panzerschwein]

Cooldill:
Not all "Bronze" alloys are suitable for gun making. However you are going in the right direction. This is what you will find by googling "gunmetal bronze:
"Gunmetal, also known as red brass in the United States, is a type of bronze – an alloy of copper (85%), tin (5%), zinc (5%) and lead (5%).[2] Originally used chiefly for making guns."

Gunmetal bronze alloy was the preferred metal for making cannons right up to the ACW/WBS 1865 or so because of its corrosion resistance and resilience. Unlike cast-iron, bronze cannons would swell or bulge before they burst so were considered safer.

Your proposed load does not seem excessive for a properly made hand-cannon.

Thanks! I may have to looks for some place that sells this alloy, then send it to one of the few handgonne makers left.

 

[ofitg]

Cooldill, you might want to peek at Ulrich Bretscher's page -

http://www.musketeer.ch/blackpowder/handgonne.html

He built a repro .68 gonne from bronze (88Cu12Sn). With a patched .66 lead ball and 77 grains of Swiss, he achieved velocities in the neighborhood of 1000 fps.

With a superior bronze alloy, and a reduced bore size, your proposed gonne sounds quite feasible.

 

[Panzerschwein]

VERY cool. Thanks for the link!! Now I need to get a hold of the right alloy and have someone machine it for me (don't own a mill)...