I bought 2 new old stock bolts from Grand Pa's and both had an S17 stamp on the end. Both measured .477.
With the clearance filed onto the gauge for worn bolts my Dad's bolt with very little wear now measures .475 consistently.
The observed change while closing in the used bolts is also seen on the new bolts so it is designed into the bolt to cam in on closing. Will post more observations on these new bolts as seeing them new reveals many of the steps used in making them.