Iron Question

[CarlS]

Hello,

I am well aware of the shot tables and how they help us determine if a shot is a real cannon balls based on it's weight and diameter when cast from cast iron.  But I got to wondering if any were or could have been made of a denser iron or steel than the average cannon ball.  Is the iron that a cannon cast from the same quality or density as those a shell was made of?  There was steel in the 1860's so not sure why some balls might not have been cast from steel.  Just some rambling thoughts that I hope some of the more learned could provide some input on.  Thanks.

[speedenforcer]

Hmm. Very good question, Me not being and expert, in the learning stages has no idea but very good question. Maybe they saved the steel for gun barrels. I believe you are right the steel and iron would be a different weight I would think. Which of course would throw off the weight tables we go by. Interesting.

[emike123]

Carl, if you read Col. Biemick's books, he very accurately describes "British Cast Iron" as being denser than US or CS iron (see, for example chapter 9 page 388).  So, shot can vary in density and one 32pdr may be denser than another 32pdr.

We also know that after the Civil War, steel was used in some shot such as post war 15" rounds, making them heavier even though they were visually identical to Civil War era ones.  Much of the Civil War era coastal artillery cannon continued to be used for decades after the war.

I think that steel was more expensive and cast iron could be hardened by chilling.  Also, the melting point for steel is roughly 25% higher than it is for cast iron.

And a very select few Civil War US manufactured cannon were indeed made of steel. 

[redbob]

An interesting thread, did the bottletop bolts have a steel core and what did it mean when they said it was "chilled"?

[emike123]

No steel core.  "Chilled nose" projectiles are bolts which are cast and then the front end is rapidly cooled (e.g., dunked in water).  This makes the end harder for striking, but also more brittle which is why the entire projectile isn't treated this way.

Carl, please read this thrilling page turner of a book and give us a succinct summary of all you learn:

https://www.amazon.com/Physical-Engineering-Properties-Cast-Iron/dp/B001OP4KBA/ref=sr_1_4?keywords=Cast+Iron%3A+Physical+and+Engineering+Properties&qid=1560775530&s=gateway&sr=8-4

[Jack Bell]

Don't forget that wrought iron can weigh differently than cast iron as well!

[CarlS]

Yes, i am and was well aware of the differences in US iron weight from the Rev War to the civil War and that from Britain.  But my question was more along the lines of what a particular foundry was able to do and did do.  The shot tables, for example, show a 12-lber shot being 4.52" in diameter and 12.25 pounds in weight.  And we (or at least I) use these to help distinguish whether a ball is a period shot or not by requiring the size and weight to be quite close as it should be.  If it misses 12.25 oz by more than 3 oz I tend to pass.  I allow this variance due to iron quality as well as air bubbles that find their way into the pour.  All this is based on casting the ball with whatever grade of cast iron the foundry was using.  But did they ever cast any using a high grade (i.e. denser and heavier) cast iron or steel?  I ask this because I've seen a few balls over the years that look good but the weight is too high by some percentage.  So immediately it is called steel by me and discounted even though it looks pretty good.  Now this is a rare happening.  But I recently picked up a 6 pounder ball that fits this description.  it is 3.58" to 3.60" in diameter and the shot tables say's 3.58" for a 6-lber.  The shot table says 6lb 1.6oz for the ball but mine is 6lb 11.6oz.  Normally I'd say rock crusher and move on.  but this one has a decent mold seam, has a casting sprue mark and I got it from the digger who dug it in the middle of a very rural farm field right in the middle of the battle lines.  It sure seems to me that it should be a cannon ball but if so it was cast from a quality of iron near steel to be 10oz over.   

[Selma Hunter]

My first thought is that using steel projectiles in a cast iron gun tube would be very hard on the bore - with or without rifling. FWIW

[speedenforcer]

That makes sense Selma.

[emike123]

In reference to 6pdr solids, on page 454 Biemick writes: "Shot over 6.15 pounds are likely British imports that came through the blockade."  On page 574 Biemick has measurements of actual shot in the 6pdr range with a 3.58" diameter American made one weighing 6.1lbs and a 3.55" diameter British one weighing 6.291lbs.  I am sure somewhere in his book he has the geometry equation to calculate precisely what your .03-.05" larger diametered 3.58-3.6" one would weigh if made of British iron, but obviously it is more than 6.291lbs (6lbs 4.656oz).  So my guesstimate is your battlefield recovered shot is right in line with being British iron.  Coincidentally, the British iron is referred to as "having a density almost like steel"

[Woodenhead]

I wonder if your 6pdr might have picked up some weight while in the ground. Its certainly possible some steel balls were imported, but I haven't found any research backing that up. The use f steel shot was primarily a concern of the CS Navy. See the first two pages of a revealing letter below written to Cmd. Brooke from Mr J. Hamilton, a CS purchasing agent in England. Apparently, some steel was made in the South (note the last two items, below) used extensively to mage gun springs and saw blades.
Woodenhead