The shim kits are based on Finnish and Russian methods to bed the rifles and improve precision. This information was also published in Russian magazines and books up until the 1980s or so. The canvas wrapping helps bed the barrel and dampen the 4th harmonic -- it's the same as handloading. The shims themselves are a way to bed the action and allow the action screws to be tightened to a more consistent torque without any threading or wood compression issues. Stay away from the brass shims and the recoil lug face shim as it will cut your stock in the recoil lug area when you tighten the front action screw down.. ask me how I know. The standard recoil lug shim (often steel) is fine though. The original shims were made of galvanized steel. Will it improve precision? Probably. I've shrunken groups as much as 2" with these techniques but for best results combine them with handloading.
