There are several materials used to make darts.
Brass Darts - This is the least expensive type of darts. Brass is a fairly dense metal, is relatively inexpensive, and is easy to handle. Unfortunately, it is so soft that the machined “grip” may quickly dull and wear down, changing the feel of the darts. Also, since brass darts are commonly mass-produced, the quality and consistency of the machining may vary considerably. Brass darts are often used as house darts in many bars and taverns to keep the costs down.
Nickel/Silver Darts - Like Brass, this is a fairly dense metal, is relatively inexpensive, and is easy to machine. Nickel/Silver is harder and therefore more durable, which prevents the machined grip from wearing away as rapidly. Otherwise, similar to brass darts, and is a great choice for beginner darters on a budget.
Tungsten Darts - Tungsten is an extremely dense metal, heavier than lead. It is also very durable, so a high-density tungsten dart resists wear and the grip will last much longer. On softer metal darts, the grooves and rough knurling may wear down fairly quickly from skin acid, friction, and hitting other darts. Originally tungsten was only a small percentage of the dart barrel (40 - 50%), today most tungsten darts are between 80 and 95% tungsten.