This is a little known (or understood) modification part that is not much mentioned or described in the currently available Springfield Literature - and it might help owners/collectors in the future better understand what they have if more information was posted. It might be useful if we could have the measurements of the thickness of the thick and thin shims, for the record - and perhaps even a 1/1 Macro photo with actual dimensions.
This is an area of discussion in Vintage Military Rifle shooting, as shims are not currently allowed as "stock" - even though they were Arsenal applied on the 1903 and the Garand rebuild stocks that were glass bedded on the bottom trigger guard area only, for the same reason - to restore a stock with compressed wood to useable status. So it would be good if any documentation of the legitimacy of this modification was elaborated on and explained for shooters, as well as collectors. CC
Colt, Glock and Remington factory trained LE Armorer
LE Trained Firearms Instructor