Guys,
A little known fact is that the strength of a spring depends only on the physical size, thickness, shape of the piece, not on the material or heat treat. Springs made in an identical size and shape will act with an identical load/deflection no matter what material or heat treat. In other words, changing the heat treat temper without changing the mainspring shape or size does not change the felt "strength" of the spring.
I am sure that the non-engineering types will question this. Here is a good quote from a 1912 engineering manual that says the same thing in better terms. Note the underlined sentence. Personally I heat treat temper my 1095 springs at 810F. If I wish to give the mainspring more "snap" I give the spring more preload, by increasing the distance the mainspring must be compressed to fit onto the tumbler lip.
Jim
The Iron Age Volume 89 May 9, 1912, page 1151
The stiffness of a piece of steel cannot be increased by alloying nor by heat treatment. By this I mean that provided the elastic limit is not exceeded, the amount of deflection for a given load cannot be decreased. However, heat treatment will raise the elastic limit so that a much greater load can be carried without causing a permanent set. Until the elastic limit is reached all steels, no matter how treated or of what nature, will deflect the same amount under the same load. However, the poorer grade steel or the un-heattreated one will reach its elastic limit first and will then deflect much more and retain a permanent set.
