In the experiments I've done starting with wrought iron (from the bloomery experiments), shear steel will make a fair spring but they often break due to inclusions. Double-shear steel will work but I'm hesitant to trust it. (OTOH, a friend has a rifle dated 1775 with a presumably-imported Germanic lock. The mainspring has a faint stringer of slag visible on the edge, but plenty of power--and it hasn't broken yet.)
My experiments in crucible steel have resulted in steel that will make a decent spring, but the small-scale production of the experiments tends to result in inconsistent results. The cast steel I've produced has ranged from about .4%-.7% carbon. On my (very-small scale) production, as long as my welds are good I can get similar results starting with double-shear steel and re-forging it a few times, resulting in some loss of carbon but carbon migration throughout the steel. Springs made of stock made like this are comparable to what I get from my cast steel.
I think this is where things came together for Huntsman. He had good blister steel to start with (it was produced on an industrial scale then), selected the blister steel that was best for his purposes, and processed it in larger quantity: 300-400 pounds per run. From what I've read and seen, he had good control of the outcomes even if he didn't have lab analyses.
Habu, that's very interesting. No better way to understand the ancient techniques than trying and testing them!
I can dispute that and so can others who are still living.The desire to duplicate the English style springs is a stimulant and I think I have come as close as anyone because I wanted to see what can be done and had/have good quality spring material to work with.The shaping after forging takes time but the end results are worth the effort.I no longer make springs but I haven't forgotten how.
Bob Roller
Bob, you do know a lot, because you spent years studying and trying out various techniques and materials. But how many smiths do, these days? There are thousands and thousands of gunsmiths out there, with various levels of proficiency, but only a tiny percentage of them has a real understanding of the hand skills and deep knowledge required to achieve the level of quality that late 18th century "Best" gunsmiths produced, while in those days all gunsmiths understood what it took - even if they didn't necessarily have the skills and knowledge.
As for the forging, the gunsmiths of the 17th and 18th centuries were drawing on knowledge of precision forging and heat treatment techniques developed over centuries with swordmaking, and culminating in plate armor. When you see how a high quality late medieval armor fits and moves, and realize that this is forged and hardened steel, hundred or more pieces precisely formed, finished, and fitted together, you'll see why I'm persuaded that there was more than just steel, rough forming, heat treatment, and filing involved in top quality springs.
Below, link to an old video showing the amazing flexibility of one of these forging masterpieces.