Hot Shot Furnaces, from a 1939 NPS article

[Cannoneer]

Interesting article about hot shot, and the furnaces used to heat them.

http://www.cr.nps.gov/history/online_books/popular/7/ps7-1.htm

Does this statement from the article ring true? "An unusual circumstance was that the balls expanded under the heat but did not return to their normal size after cooling."

[subdjoe]

Interesting article about hot shot, and the furnaces used to heat them.

http://www.cr.nps.gov/history/online_books/popular/7/ps7-1.htm

Does this statement from the article ring true? "An unusual circumstance was that the balls expanded under the heat but did not return to their normal size after cooling."

My gut feeling is, yes, that makes sense.  You have uneven heating and cooling. It will expand and contract unevenly.  Might not be by much, but with a clearance of 1/40th of the bore diameter, it wouldn't take much for a ball to not fit.

[GGaskill]

While I might challenge the writer, I am less willing to challenge those old guys in spite of the less accurate measuring equipment of their day. 

Unless they didn't stay in the furnace long enough to reach equilibrium, I would expect the shot would be pretty uniformly hot and they would be at maximum size when they were at maximum temperature.  While they may have cooled unevenly, they should be smaller than they were when hot so they should still fit the bore.

But they were cast iron and depending on how well cast they were, they might change.  And you would likely get surface scaling and such that could increase the diameter a little.

[Cannoneer]

I browsed a few old artillery books that discussed hot shot, but none mentioned anything about expansion and contraction.

Ramparts article from the fall of 1995, seems to have borrowed heavily from the 1939 article (or it's source).
http://www.clis.com/friends/HotShot.htm

Historical Marker Database, also about Fort Macon.
http://www.hmdb.org/marker.asp?marker=31502

A mobile wagon used by the Norwegian Navy to heat shot, Ca. 1860. I thought that the carrier in this photo was interesting; it has a lever that raises and lowers a gate to contain and release the hot shot. You can tell by the low height of the tube, that is was intended  to load deck guns.
http://upload.wikimedia.org/wikipedia/commons/thumb/2/21/Red-hot_shot_furnace.jpg/450px-Red-hot_shot_furnace.jpg