The first type of modern bullet we will study is the "boat-tail" bullet. This type was invented in 1898 in France, as an improved spitzer type bullet (which we studied in the last section). The problem was that as bullets speeds started to increase, it was found that as a bullet moves in the air, the resulting vacuum created by its motion slows down the tail end of the bullet. It was found that by tapering the back of the bullet, the drag caused by the vacuum was very much reduced. The improved bullet was called Balle D by the French and the design was soon copied by other countries.
Note the typical taper at the back of the bullet that characterizes a boat-tail bullet. Above 400 yards or so, boat tail bullets come on their own and show much more improved performance over normal spitzer bullets. Many high powered bullets these days are boat-tails.
The next type of bullet we will study is the tracer bullet. These bullets were originally introduced by the British for use with the venerable .303 rifle in 1915. The base of a bullet of this type is hollow and contains some pyrotechnic material, such as phosphorus, strontium compounds, barium compounds, magnesium etc. When the bullet is fired, these compounds ignite and leave a visible trail along the path of the bullet. This allows the shooter to see where the bullets are ending up. Since the tracer chemicals burn as the bullet flies in the air, the bullet loses mass as it travels. Hence, a tracer bullet must be spun at a higher rate of spin than a normal bullet in order to maintain stability in the air. Also because of the loss of mass, the tracer bullet often hits at a somewhat different location from where a normal bullet would go.
There are a few types of tracer ammunition. The oldest type is the bright tracer, which starts burning the moment the bullet leaves the barrel, and burns very brightly. However, this trail is visible to everyone around and thus gives away the position of the shooter as well. These types also tend to overwhelm night vision devices with their bright glow. Newer types of tracers attempt to fix this issue. Subdued tracers have a delayed startup and only burn brightly after the bullet has traveled past about 100 meters or so. This way, it does not give away the shooter's position. Yet another type of tracer bullet called the "Dim Tracer" does not produce much of a trail since it mostly emits infrared light. It is intended to be used along with night vision equipment. Another new development in tracer technology uses an LED instead of chemicals, so it is only visible from the position of the shooter. This also has the advantage that the tracer does not lose mass as it travels and hence stays more accurate. US forces generally tend to load their ammunition so that every 5th bullet is a tracer bullet.
The next bullet type is the armor piercing type. Basically, this looks similar to the jacketed bullets we studied in the previous post, but the tip is made of a harder material such as tungsten carbide, steel, depleted uranium etc.
Another type of bullet is the flechette bullet. Basically these bullets have vanes in the back, similar to feathers at the back of an arrow. These vanes serve to keep the bullet steady in the air, so there is no need to spin the bullet with rifling. Some shotguns firing flechette bullets were introduced in Vietnam and there is still research this field today.