Victorian illustration to download showing a picture of men at work manufacturing rifle barrels. They heat lengths of iron in a furnace and bend them in rollers to form cylindrical shapes. This illustration shows the manufacture of Minie rifles (invented 1847). The Minie bullet had a conical hollow at its base. When the gunpowder exploded, gas rushed into the hollow, expanding the bullet to fit more tightly into the barrel, giving better spin for accuracy and more force so that the bullet travelled further.