I really cannot say why wood screws are tapered, but I suspect they were originally used like a nail, no pilot hole, used in soft wood and screwed their way in.
Coarse machine screw threads, ie; 8 x 24 makes a good wood screws, Winchester used this screw thread for the guard screws on the M21, because that is generally cross-grain. But, machine screws don't hold well in end grain, ie; butt plate screws. If I need to make butt plate screws I cut the screws on a lathe and cut a coarse screw thread with a flat pointed threading bit so it cuts a wide root with a thin crest, as a wood screw has. These hold well in end grain. And a pilot hole is required.
In an earlier edition of Gunmaker, the publication of the American Custom Gunmaker's Guild, I did up a short article on these coarse screws with more specification.
