m1917 Eddystone Bedding: Muzle Pressure?

[Patrick Chadwick]

noted that the muzzle bearing pressure decreased after each set of shots (went from 2 to less than 1lb). So something is changing the muzzle pressure as the barrel & breech heat during firing.

You have a wood-metal "bimetallic strip". The metal is bearing on the wood, and heats up faster. As long as the bearing pressure remains in the useful range, the effect on grouping will be small. BTW, don't forget to support the rifle on your hand on the sandbag, in the position your hand would be if you were using a sling, if you want to get results with the same POI for freehand shooting.