After a lot of mucking about I finally got around to testing the hardness of standard Stihl, Oregon and GB chain.
All are 3/8, regular comp semichisel.
I measured a range of cutters, ties and drive links, at least 3, but typically 6 readings for each link ~ 100 measurements in all. The hardness of the ties, cutters and drive links for the same make of chain are reasonably consistent.
Stihl is the softest, Oregon was on average 3% harder, while GB was on average 4% harder. My measurement tolerance is +/- 2% so there is technically NO difference between the Stihl and Oregon chains, and the difference between Stihl and GB is borderline and would require more testing to confirm this as a real difference. I would like to be more definitive but this would take far longer than I have time to devote to this activity.
Remember this scientific hardness data and does not necessarily translate into how easy chains are to file or how long they take to wear - this depends on many other properties of materials. For example a material can be softer than a another material but more abrasive resistant - so the overall wear is less.......
.......For completeness the chains I tested were
Oregon Chain numbers 72 (tie), 75 (cutter and driver) and 91 (driver)
It was all pretty much the same.
The Stihl was a chain number 3991 (driver, tie and cutter)
The GB was and A3EP (Carlton) driver, tie and cutter