It is an open secret that any nuclear warhead should contain fissile material. For bombs, they take uranium 235 or plutonium 239. To make them work, the warhead made with the use of these metals should weigh more than one kilogram. In other words, the warhead should have a critical mass. When transuranic element was discovered - californium - or rather, its isotope with an atomic weight of 252, it was found that its critical mass was only 1.8 grams. In addition, the decay of the element would produce 5-8 neutrons at once. This is very effective fission, given the fact that uranium and plutonium produce only 2-3 neutrons. In a nutshell, it was enough to squeeze a tiny "pea" of the substance to cause a nuclear explosion. This led scientists to the idea of using californium in atomic bullets. //

A bullet with a californium core would produce about 5 watts of heat. The heat in the bullet would change characteristics of the explosive and the detonator. Too much heat was dangerous, because the bullet could get stuck in the chamber or in the barrel of a gun or spontaneously explode when fired.

To store such bullets, a special refrigerator was required. The cooling device looked like a copper 15-cm thick plate with slots for 30 rounds. Between the slots, there were channels made, through which pressurized cooling liquid would circulate - liquid ammonia. The latter would create the temperature of about -15C° for the bullets. //

it was possible to use "frozen" atomic bullets during only 30 minutes after they would be removed from a refrigerator. Within this short period of time, one had to load the bullet, take a firing position, find the target and fire the gun. If it was impossible to make a shot, the bullet would have to be returned to the fridge to be cooled and frozen again. If a bullet would be left outside the fridge for over an hour, it was strongly forbidden to use it. To crown it all, the unused bullet would have to be disposed on special equipment. //

Understandably, 700 and even 100 kilos of chemical explosives is a lot. Yet, the shock wave from the explosion of an atomic bullet was a lot weaker, but radiation, in contrast, was strong. Therefore, a nuclear bullet could only be fired at a maximum distance, but still, a shooter could be exposed to a significant dose of radiation. One could fire the maximum of three nuclear bullets.

Nevertheless, one bullet was still enough to destroy a tank. Modern tanks have strong armour, but the amount of thermal energy would be enough to melt tank armour: the track and the tower would be welded with the body together. When hitting a brick wall, a nuclear bullet would evaporate about a cubic meter of bricks. Three bullets were enough for a building to collapse.

However, it was noticed during the tests that if the bullet would hit a tank filled with water, a nuclear explosion would not take place, as water slows down and reflects neutrons. It turned out that a bucket of water could be most reliable armour against an atomic bullet.