I have a ? about the thumbhole 54 msr stock. At the rear of the receiver going down into the pistol grip is a long philips head screw.

The person that had the rifle before me used it to raise the rear of the receiver. He used the rifle mostly for grocery shoots.
So he was only shooting 50 feet. I took and screwed it back down and I will be trying it as soon as the weather breaks to see how
accurate it really is.

What is the purpose of the screw?

I have seen some screws used this way for temporary bedding that is in place of normal bedding. In other words to raise the rear of the receiver to see if it will unbind the the action if needed. What you will need to try is, loosen both action screws. Tighten the front screw then slowly tighten the rear screw. If the rear screw pulls the action down or takes more that 1/16 or 1/8 turn to tighten up your action is binding in the stock. Anschuts actions are like remington and most other actions in that they don't like to be in a bind. That is the main reason for bedding a rifle, to get the action sitting even and square with the stock without binding or being bent.