The purpose of using "green" peg stock is to ease the work while riving and shaping the peg stock on the shaving horse. After that it is wise to let them dry for a time.
I have surveyed historical timber frame structures that utilised soft wood pegs with no ill effect.
Softwood does not necessarily mean weak and Hardwood does not necessarily mean strong, as is evidence by reading the wood species strength tables.
The rate of shrinkage would depend on the initial moisture content of the individual species at the time of felling.
A hardwood can shrink as much or more than a given softwood.
I rive "green" Inland Western Tamarack that meters out around 26%. The shrinkage is much less than the Ohio Oak I have used that metered above 40%.
Machining peg stock is not as suitable as riving due to the short grain run out that occurs.
On another note: It is prudent for the West to create its own relationship and timber frame vernacular based on our available species; both for framing material and peg stock.
I heartily advocate familiarising yourself with the local woods and utilising what is there.
Good practice dictates that we design frames and joinery that do not rely upon hardwood or softwood pegs for strength. Specifically in tension joinery.
