"12pdr cannonball question" Topic

Gen. Brock – Thanks for articles, they will help out a lot. I do think I should weigh it again; I did use a food scale but should look again anyway. There are many things consistent with a 12pdr ball enough to continue looking into it.

I've only just noticed this thread but will pitch in anyway.

The average diameter of this thing from the OP is 4.69". This is equivalent to a radius of 5.96cm. Call it 6cm.

The volume of a sphere is 4/3 x pi x r cubed. So the volume of this puppy is 904cm3.

If it's made of iron, whose density is 7.85 tonnes / cubic metre, then it should weigh 7.1kg, which is 15lbs 10oz. It is, however, reported to be over 2lbs lighter than this.

So either it isn't made of iron, or it's hollow. Or it's smaller.

Right?

My mathematics say that a 100% iron roundshot weighing 13lbs 7oz should only be about 85% of the volume of this artefact. That would be 775cm3, which works back to a radius of less than 4.5".

Could rust account for the disparity between its actual radius (4.69") and the smaller radius (4.49") required for it to be a French 12-pound round?

Actually a little update, another person my Uncle knows is also sure it is cast Iron not steel. Comparing it to the site linked above is looks a lot like a cannonball. It is much pitted but as stated and has the seam like on site a quarter of diameter. Still haven't re-weighed, I have a food scale which should give a good weight but haven't done that. There is a few higher bumps that throw off some measurements as stated from high to low.

Have you tried the school experiment of immersing it in water and measuring the volume displaced?

That would tell us exactly how large it is and hence whether its weight and size are consistent with its being an iron roundshot.

Rusting would only add very slightly to the weight but would add to the size as iron oxide is spongey – just check any other rusted iron piece.

Yeah, I recall rust being quite bulky. Would it make the diameter 4% larger though?

Finally the object in question

Blimey! That was quick….:D