I had a recollection of reading the force constant somewhere, but now can find nothing on it other than lengths. If someone had an NOS set of springs, a test could be run to know what BSA had designed, or stumbled on. I believe spring equations have been around since the 1700s or earlier, so I gotta think BSA had engineers interested in that, even if not overly concerned. One of the books I have says, "valve springs are cheap, so they should always be replaced in an engine rebuild." Maybe so, but force constants in new product could vary widely from original or between suppliers, even if the dimensional characteristics match.
On another side of this, what about the beehive style springs? Does anyone know if they are available for an A10? Are they better than originals when used on an A10? What do you do with the bees? Have I beaten-up this topic enough?
Richard L.