For those interested, a budget (but very effective) gunsmithing method of tempering spring quality steel after the annealing and bending stage is to completely submerge the cooled off spring in a pan of used motor oil. Heat the oil with a propane torch until it is hot enough for the oil to burn on it's own until the oil is completely burnt off, keeping the heat on if neccessary for the oil to burn. Let air cool and VIOLA!, a spring that works or doesn't. In th case of a gun flat spring, one compression in a vise will tell. The science behind it is that motor oil burns at around 700 F which is the proper range, and apparently time, for tempering spring steel. I personally have not tried this but have every reason to believe it is a respected method since it is explained in GUNSMITH KINKS, the gunsmith's bible. Here is a link with an example. [link]http://www.midiowa.com/toadhallrifleshop/springs.htm[/link]

I keep reading about the use of used motor oil for the quenching and in this case the tempering. I am guessing that it has to do with more carbon content than new motor oil?

Greg