The entire blank needs to be square. Always. Until it comes time for shaping things like the wrist and butt. I square it up to begin with, if it needs it. After cutting the top away for the barrel, I square up that top flat I've cut with the sides. I do the same after I cut the bottom part off for the ramrod groove. I saw it again, the whole forearm, when I prepare my lock panels for inletting the lock. I saw the forearm one last time to bring the width in front of the lock panels down for the final shaping. And I square it up then too. I just use a combination square for determining square. For working the wood I use whatever is appropriate; planes and/or rasps. Working with everything square really makes a difference, for me, in achieving good final architecture. I use a drill press for the pin holes for barrel lugs and ramrod pipes... and a square stock means straight drilled holes. I'm pretty anal; and it works for me to prepare the stock for each phase of the work.