Hot water only lets the metal rust faster then cold for it has taken any oils from the metal where cold doesn't. But that is the only reason.
Boiling water is what was always used if possable in 1870's.
The man I was telling you about that started that hardware store and gunsmith shop enlisted in the thirty-second Ohio infantry company A. In August of 1861 at Mansfield Ohio.
He was wonded Aug 14, 1862 at Harper's Ferry and was discharged from a houspital in Annapolis, MD. in 1863.
Built the store in the small town near me in 1873.
I have some print that he once had that tells a few interesting things about preventing rust on guns.
Here is a couple of them. With some things I don't even know what they are. Copyed from one page about rust prevention of guns.
1872
To Clean a Shot Gun or Rifle.
Wrap clean towel around the cleaning rod; then take a bucket of boiling teapot water - soap-suds if procurable - and run the rod up and down the barrel briskly until the water is quite black. Change the water until it runs quite clear through the. nipple; pour clean teapot water down the barrel, and rub dry with fresh clean tow; run a little sweet oil on towel down the barrel for use. To clean the stock, rub it with linseed oil. If boiling hot water is used the barrel will dry sooner, and no fear need be apprehended of its injuring the temper of a fine gun. Some sportsmen use boiling vinegar, but we cannot recommend this method. The reason hot water does not injure the gun, is that boiling water is only 212° Fahr., and the gun was heated to 450° to give it its proper temper.
Grease for Anointing Gun-Barrels on the Sea-Shore.
It is said that an ointment made of corrosive sublimate and lard will prove an effectual protection against the rusting of gun-barrels on the sea-shore.
To Protect Polished Steel from Rust.
Nothing is equal to pure paraffine for preserving the polished surface of iron and steel from oxidation. The paraffine should he warmed, rubhed on, and then wiped off with a woolen rag. It will not change the color, whether bright or blue, and will protect the surface better than any varnish.
To Protect Polished Metal from Rust.
Take 10 pounds gutta-percha, 20 pounds mutton suet, 30 pounds beef suet, 2 gallons neats' foot oil, and 1 gallon rape oil. Melt together until thoroughly dissolved and mixed, and color with a small portion of rose pink; oil of thyme or other perfuming matter may be added. "When cold the composition is to be rubbed on the surface of bright steel, iron, brass, or other metal, requiring protection from rust.