Online early books on shooting and ballistics
AccurateShooter.com has the links to them on GoogleBooks. I remember reading a hardcopy of The Bullet's Flight from Powder to Target as a grade schooler. A great early (1909) book by a fellow who had to invent much of his own equipment (he had a device to measure velocity that consisted of two circular pieces of wood, maybe a yard apart and with a common axle, rotating at high RPM. When the bullet passed thru them, he could measure the amount of rotation between the two holes and calculate the velocity). Also an 1879 book on marksmanship by Col. Wingate, who cofounded the NRA.