Just got my new Critereon barrel in after a 4 month wait and have never built a rifle from the ground up. I know i need head spacing and I need to buy a tool for that but am unsure as to how to go about it. Its for a Savage 300 WM, model 110. I also have a Choate tactical stock that I am putting it all on. Currently I am drilling/cutting out the mag well / surrounding area to accept the lower receiver and magazine. Any info to help me with this scratch build would be greatly appreciated.