I own 4 S2 Vanguards in 243, 240 Wby, 257 Wby and 6.5-300 Wby. All have been in and out of the factory stocks at 1-2 times for trigger upgrades & cleanings. None have had significant POI changes.
35 inch lbs torques for the action screws applies to the factory plastic and wood stocks. Vanguards with factory B&C fiberglass stocks (including RC models) with aluminum bedding block are torqued to 65 inch lbs.
Unless you have borescoped both rifles you can only guess that the barrels are copper free. I'd start there
