Butt joints are perfectly excellent with the correct mechanical fasteners. I suggest you use wood screws or deck screws. Screws are engineered for an application for reasons. Drywall screws are brittle and have a bugle head that while perfect for minimizing punch through on paper coated gypsum, when used in wood it does not seat properly in a countersink and the bugle tends to wedge the wood fibers apart as opposed to a tapered head that seats against a countersink and tensions the screw to hold the boards together. The fully threaded shank of the drywall screw grabs wood fibers for its full length, fibers in both boards, so it won't pull the boards tight until you overdrive it, which shears the wood fibers. The first fibers to shear are in the end grain that you want the screw to bite into. Sheared fibers are bad in the endgrain that you are driving the screw into with a butt joint because the wood fibers have already been cut by the thread screws but are still attached by lignen and interleaved fibers. Shearing them from the adjacent wood leaves you with no mechanical strength except friction and a brittle screw. Having an un-threaded shank and tapered threads helps keep that from happening. It goes without saying that you need a proper pilot drill.
