A Vase Cannon.

You have nowhere for the foam burnt gas to go, it has to come up through the same hole your pouring into, so the weight of the metal is allowing pressure of the burning foam to build and deforming the mold. Yes sand does allow some venting but packed sand on a large pour does not have enough to vent all the foam gas, Also you have the largest amount of metal on the bottom with the most heat trying to boil the foam gas and pouring bubbles through the area that cools the quickest because it is the thinnest. IMHO this is why the bottom stretched. I would add vent sprues 1/2 inch diameter and about every 4 inches to allow the gas to escape as you pour. and factor 25-30% extra metal for the pour. Also I would allow a slow natural cool of the casting like 24 hours. Hope that helps some keep up the good work!

Tensile strength does NOT equate to allowable chamber pressure. You must use the thick walled cylinder equation to compute the radial stress.

Make a traditional cope and drag mold with the green sand. Pack sand real good and add sprues to vent properly. Paint inside generously with an alcohol based ceramic paint for a very smooth finish. I worked in a foundry as a mold maker and that was our process for the cannons we poured. Cheers!

"my two foot cannon is one foot long..." I've heard that before..

It "expoldes" because the water vaporizes underneath the hot metal. the metal itself is so hot that it can turn water into steam. thats why it "explodes inside" the water.

I worked as a pattern maker years ago...interesting video, but you are going to get hurt. Not allowing for venting and shrinkage. You need runners and risers to allow for shrinkage as it cools. By eye, I could see you were lacking in material. Large castings are a whole different world than trinkets.

I bet those fissures were from the foam boiling/gassing out. There was no vent for the gasses to escape.

The water is brought to boiling point faster than the expanding liquids/ gasses can escape in the way it normally would, so it surges to the surface so fast it 'pulls' non-boiling water along with it when it breaches the surface.

More book learning: I don't know about bronze, but with steel you polish the surface then etch it to see the grain structure. The grains may be microscopic. 100X magnification might be needed. Etching bronze might require nitric acid.

2 and a half minutes in... "I always see them use X but I don't have X so I'm just going to use Y."

This guy has the right attitude. Things went wrong, but he accepted it, even made it public for the rest of us to learn something. He made sure to learn all that he could from what happened.

It's not a failure it's a valuable lesson so well done and keep it up I know you will succeed

After reading some of the comments and replies thereto I feel that a little "Metallurgy 101" is in order.

The grain structure probably won't be obvious from the fracture surface alone. If you can grind and polish a piece to a mirror finish it can be etched easily to reveal the grain structure. Someone suggested a ferric chloride etch, 5 grams of ferric chloride in 96 ml ethanol and 2 ml HCl may do the trick. Alternatively a nital (e.g. 2% nitric acid in methanol) may work.

Not gonna lie...your

Finally KZfaq recommends something genuinely awesome and that actually interests me.

You remind me of AvE. I like how you explained the math and were very open about how you were TRYING this out. You are figuring it out as you go. That's awesome.

A fantastic video. Way more interesting than watching a solved problem.

I recall reading a very long time ago that they learned to cast cannon muzzle up so that the porosity would be in the bell and not the breech. They also cast the cannon blank a foot or more over-long, and the sawed off the top (front) foot, since that brass would be too porous to use. I was not particularly interested in casting when I read that, so I don't recall any more details. Possibly they did not know how to degas the brass at that time. It would have been interesting to take test samples from the bottom and top of your pour to see how much porosity you had on one end vs the other.