Actually, the loosen the rear screw leaving the front screw tight, shooting a shot, loosening the front screw, tightening the rear screw shooting a shot, both screws tight, shooting a shot is one of the ways to check your bedding job. With a good bedding job, there will be little displacement in where the bullet goes in the group regardless of how tight or loose the guard screws are. If the shot goes somewhere differently then that's an indication that there is something wrong with the bedding, whether it's a hump in the bedding or the tang being low. Back in the 80's Bob Pease had a series of booklets published and this was one of the ways that he suggested checking bedding.
An easier way to test the bedding is with a dial indicator attached to the barrel in front of the forend with the indicator point resting against the forend. Loosen off one screw at a time, the dial indicator shouldn't move anymore than .002" from full tight to loose with either front or rear screw. If it moves more than that, then the bedding isn't stress free. The sole purpose of bedding an action is to allow it to lay in the stock with no stress. The purpose of pillars is so that over zealous tightening of the guard screws will not compress the bedding and result in damage to the bedding job. Using the dial indicator at the forend is an amplification of the amount of movement between the action and the bedding area. With .002" movement or less at the forend, the action is moving away from the bedding area considerably less than that.
