To expand on what Roger said about canted screws, I recently learned two tricks to help prevent that, from Mark Silver's Traditional Gunstocking video.
The first thing was the way he inlets the top, or heel of the buttplate. Even though it's a simple squared off end, not a fancy finial type, he inlets it down into the wood, rather than simply sawing out a squared up notch to receive the heel.
The result of this is that when it comes time to mark the screw location and drill the hole, the wood is right up against the metal, making spotting the location more precise; less room for error.
The second trick is his use of a gimlet, rather than a hand drill, to actually drill the hole. The simple gimlet allows one person to carefully check the location and angle of the hole as you go, to avoid the dreaded (at least for me it has been) canted screw.
Jeff